He was offered a medal, praised highly, and invited to the orgy. He let his pilots indulge because it would be inhuman to deny them pleasure just before they're sent to die. But he's not happy.
"In all my travelling throughout the universe I have battled against evil, against power-mad conspirators. I should have stayed here. The oldest civilisation: decadent, degenerate, and rotten to the core!" —The Doctor, Doctor Who, The Ultimate Foe
Ralph in Soukou No Strain goes to the Deague before the series because, it turns out, the Union created Strains by stealing technology from a race of eternal lolis and then vivisecting them to study their Psychic Powers and use them to make Mimics. Later on, Ralph backstabs the Deague too, and Medlock, in desperation, runs to the Union because she's appalled by him.
This is how EmmaSheen joined the AEUG in Mobile Suit Zeta Gundam, although, she actually DID agree with the AEUG's ideas because they represent the ideas she THOUGHT she was fighting for with the Titans. After the murder of Kamille's motherand being shown the colony gassing the Titans carried out before the series began, she realizes the Titans are massive assholes who only want to keep an iron grip on their power who only claim to be just defenders of peace.
In Chrono Crusade, Chrono betrayed the Sinners after Aion ordered him to kill Mary Magdalene, the girl he fell in love with. In the manga version when he first betrays Aion he hopes to go to the Magdalane Order not because he believes in their religion so much as he desperately needs their help to save someone he cared about from possession but fails to reach them in time. Both versions have him eventually joining the Order much later.
Kadota, Walker and Erika from Durarara!!. They used to be part of the Blue Square gang. Then the gang's leader (Izumi Ran) kidnapped a rival gang leader's girlfriend, tortured her, and sent a runner over to Kadota to ask him if he wanted to join in on the "fun" they were planning to have with her. Kadota and his buddies decided they weren't part of the Blue Squares anymore. In fact, they decided that there wasn't going to be any Blue Squares anymore. Molotov Cocktails were involved.
Later in the series, Izaya (under a pseudonym) incites a number of Dollars members to take two of Chikage's girlfriends hostage in retaliation for recent attacks by his gang (which were, themselves, retaliation for attacks misattributed to the Dollars). When Shizuo catches wind of this, he goes apeshit in classic Shizuo fashion before leaving the gang for good.
In One Piece, Luffy's childhood friend and blood brother Sabo was this. Even though his parents were nobles, he was aware and grew disgusted at how selfish and arrogant they could get, no to mention the entire nobility of the island crossing the Moral Event Horizon by trying to burn off a rubbish pile, which includes numerous villagers. He thus decides to run away by building a simple raft and start off his life as a pirate. Too bad he got in the way of a World Noble and his raft was destroyed by the explosion. On the other hand, the timeskip revealed that he had actually survived and is now with Dragon's Revolutionaries, meaning that his desire to leave the nobility has come to fruition.
Fleet Admiral Sengoku became General Inspector Sengoku because he was getting old and didn't want to deal with the World Government anymore, which he realized was truly corrupt when they were willing to cover up a mass breakout of Level 6 criminals from Impel Down from the public because it would reflect badly on them. Garp likewise ditched because of Ace's death. Aokiji also left after Akainu became Fleet Admiral.
This is basically Lelouch's story from the moment he gets the cold shoulder from his father regarding the death of his mother Marianne and the crippling of his sister Nunnally. The subsequent exile to Japan, and invasion of said country only cements his desire to obliterate the Britannian Empire and deliver cold vengeance to his father.
Kallen could also be considered one for her rejection of her noble Britannian lineage in favor of Japan and her biological Japanese mother as well as her brother Naoto, who died fighting the Britannian occupation.
Treize Khushrenada from Mobile Suit Gundam Wing, who defects from OZ when they embrace the idea of the unmanned Mobile Dolls and thus lose the qualities that Treize joined them to promote. Treize eventually reverses this when he takes them back over.
D.Gray-Man: As of chapter 205, Allen, having become disgusted with the methods of the higher-ups, has left the Order in order to find a better way to fight the Earl.
Yoshino Soma is this towards the Bounts in the first Filler arc in Bleach.
The Daxamites of the DC Universe, in addition to gaining powers similar to Superman under a yellow sun but with a fatal weakness to lead instead of Kryptonite, also happen to be viciously xenophobic. Future Green Lantern Sodom Yat was unique in that he wanted to go out into space. One day an alien named Tessog crash-landed on Daxam and the two quickly became friends. When Sodom's parents found out, they killed Tessog and brainwashed their own son into thinking Tessog was evil. Sodom only remembered what really happened after seeing his friend's stuffed and preserved corpse in a museum. He was so pissed off that he repaired Tessog's ship and vowed to leave Daxam forever. Then the Green Lantern ring found him. Sodom would only return to Daxam after learning from his mother (who had fled using Tessog's ship) that the Sinestro Corps invaded it. And even then he demanded that she give thanks to Tessog for providing her a means of escape. Because Sodom Yat is a Green Lantern and a hero through and through he still ended up making an apparent Heroic Sacrifice to save the planet.
Lar Gand (later known as Mon-El) is yet another Daxamite. Although his backstory on Daxam wasn't nearly as traumatic, he pretty much became a fugitive for wanting to, and escaping, Daxam to travel the stars.
Laurel Gand, Mon-El's fellow Daxamite and Legionnaire. She was indoctrinated into the Daxamites' xenophobic teachings since birth and sent to be a Sixth Ranger Traitor for her people's planned genocide against humans, but saw the light and fought back against them.
This, and maybe a touch of Defeat Means Friendship, is why Baron Soontir Fel left the Empire and joined Rogue Squadron. The page image is of him standing aloof in a celebration for a victory that he does not believe merited the name.
Of course, the fact that he married Wedge Antilles's sister probably helped the switch along, too.
Hans Von Hammer becomes this at the end of Enemy Ace: War of Heaven. When he discovers the truth about the death camps, he immediately leads his men in surrendering to the Allies, although he does destroy the prototype jets first.
Game Theory has an original character who loathes her planet's oligarchical political system, and enlisted in the TSAB at the first opportunity.
One Piece: Parallel Works: Yuki-Rin ran away from her Tenryuubito parents so she could follow her dreams of becoming a pirate, and because she thought the lifestyle of the Nobles was cruel.
In the Star Wars prequels, Count Dooku initially leaves the Jedi because he felt the organization had decayed, and were not taking seriously his warnings that the Sith were still around. Ironically, he ended up joining the Sith afterward. Which proves that they exist.
As well, the novel Death Star reveals that the Imperial gunner (Tenn Graneet) who kept saying "standing by" was actually a Rebel sympathizer; the laser was charged the whole time, and he was just trying to distract Tarkin long enough for the Rebels to blow the station up, knowing full well doing so would result in his own death.
Besides Graneet, there were some TIE pilots who decided late into the novel to defect to the Rebel Alliance. Some had to stay behind to ensure that they escaped. They would have been killed by Vader for it had he not been forced to return to the Death Star to stop the Rebel forces from attacking the thermal exhaust port.
Some supplementary materials, including the Rogue Squadron series, revealed that two Imperials defected to the Rebels' side, Tycho Celchu and Kasan Moor. Both were TIE pilots prior to defection, and both characters' motivations for defecting was largely because they are Alderaanian, meaning that they weren't too happy with the Empire for blowing up their homeworld.
A few of the more famous individuals throughout the series have also been former Imperials who left for various reasons, including Han Solo (court-martialed due to rescuing Chewbacca from a slave operation) and Kyle Katarn (defected when he learned the Empire was responsible for his father's death).
Dr. Noah and Shua in Sky Blue both left Ecoban - Noah in protest at its environmental impact, and Shua because he was framed for a murder. Jay becomes one over the course of the film, and Cade does at the very end.
Also Wheelie, due to a combination being more scared of Mikaela than he was of Megatron, and being physically aroused by her. Who isn't?
In The Wind That Shakes the Barley, a Scottish soldier of Irish parentage pulls a Mook-Face Turn and joins the IRA after witnessing the brutal treatment of the Irish by the British state; a particularly twisted Secret Test of Character, a brutal interrogation session and the planned execution of a number of captured rebels are what push him over the edge.
Isabella, the French princess in Braveheart. While it's true she never actually participated in the English atrocities in Scotland, she is nominally loyal to King Edward at first (he is her father-in-law, after all); after gradually becoming disillusioned with the motives of Edward and his allies, she begins to clandestinely aid the Scottish rebels, and ultimately bears William Wallace's illegitimate child (which was Artistic License - History, but never mind).
In the Battletech novel Exodus Road,Proud Warrior Race Guy Trent defects from his Clan when he feels it's been tainted by political intrigue. This helps set off a chain of events that leads to the utter destruction of the Smoke Jaguar Clan.
The Elric Saga: Prince Elric of Melnibone, the titular Anti-Hero and one of the incarnations of the Eternal Champion in Michael Moorcock's fantasy universe. In his case, his whole race was infamous for being callous, sadistic and decadent slaveholders (although we get to meet a few Melniboneans who are not malicious and underhanded, most notably Elric's fiancee and the pragmatic dragonriders). Elric, himself a powerful sorcerer, had grown so weary with his people's banal wickedness that he left Imrryr The Dreaming City, but later returned with a fleet of human warships to destroy it, razing the last remnant of a once proud and ancient civilization.
Dorian Hawkmoon, the Duke of Köln, another incarnation of the Eternal Champion, finds an unlikely ally in his fight for freedom in the Granbretanicaristocrat d'Averc. d'Averc is fond of affecting the appearance of a decadent effete courtier and hypochondriac to the point of cliche. However, there is every indication that it's just for show, and that d'Averc is quite tough, strong and shrewd, not to mention a superb swordsman and duelist and a Deadpan Snarker (and secret romantic). Although cheerfully untroubled by moral considerations, d'Averc is not as utterly amoral (nor borderline insane) as most of his fellow Granbretans. In fact, he seems disgusted at the decadence and violence of the tyrannical Granbretan Dark Empire, and defects to help Hawkmoon and Count Brass.
The Lord of the Rings: In the world of Middle-Earth, the realms of Arnor and Gondor were both founded by Elendil and the Númenóreans who fled with him after their kingdom was corrupted by the influence of Sauron.
OTOH he was only snatched after he was beaten and locked in a shed, which was then set on fire, by his own forces on the order of a prelate after his own less-than-controlled "witch-powers" warned him in time to rescue a Karsite hamlet from a nasty bandit raid.
Then I did not fully realize the cowardice of my jeddak, or the bravery of you and the girl. I am an old man from another age and I love courage. At first I resented the girl's attack upon me, but later I came to see the bravery of it and it won my admiration, as have all her acts. She feared not O-tar, she feared not me, she feared not all the warriors of Manator. And you! Blood of a million sires! how you fight! I am sorry that I exposed you at The Fields of Jetan. I am sorry that I dragged the girl Tara back to O-Tar. I would make amends. I would be your friend. Here is my sword at your feet.
Tom Clancy: Any Soviet defector in a Tom Clancy novel. They are usually high-ranking military officers, politicians, or KGB agents who decide that the Soviet Union is not deserving of loyalty.
In Diane Duane's Star Trek novels about the Romulans/Rihannsu, a Romulan commander named Ael doesn't quite defect, but she does make an alliance with James T. Kirk (and by extension the Federation) to prevent some truly evil actions on the part of the formerly-honorable, now-corrupt government of the Romulan Empire. She never does fully defect, but she becomes a close confidant and ally of Kirk, and it's implied that there's something more nascent between them, more than just friendship or Kirk's signature skirt-chasing.
Fidelis from the Codex Alera series initially turns traitor against Gaius Sextus when he believes that the First Lord is too weak and it's better that the strong Lord Aquitaine be in position to seize the throne rather than allow The Empire to fall apart in civil war and foreign invasion. When he learns that Tavi is the rightful heir and a hell of a lot better person than either Lord or Lady Aquitaine, he dumps them.
In the Night Watch series, two of the Dark Others, Edgar and Arina left the Day Watch, not really because of goodness, but due to a combination of growing tired of the constant maneuvering of Light and Dark against each other, and due to both of them hating Zabulon, the head of the Day Watch.
Quite a few works of dystopian fiction make the protagonist into this. In 1984, Fahrenheit 451, and Equilibrium, the protagonist starts as an active agent of the dystopian regime, but over the course of the plot turns against his society, whether successfully or not. You can almost apply this to Logan's Run and Brave New World, though in the former the protagonist is unwillingly exiled from his society while in the latter the point-of-view character introduced at the beginning is swapped for a fish-out-of-water protagonist about halfway through the book.
Raamo, Neric, and Genaa in the Green Sky Trilogy. Neric already checked out mentally, and was looking for allies. Raamo steadfastly refuses to believe he's above and apart from other Kindar, and while Neric had doubts about Genaa, she turned out to be more like her exiled father than anyone suspected. The whole thing turned out to be a whopper of a Batman Gambit on behalf of High Priestess D'ol Falla, who was looking for a way to atone for some horrible mistakes she made in her youth. The only ones who could set things right were those who could taste power and walk away from it.
The Hunger Games trilogy depicts the overthrow of a ridiculously lavish Capitol by the rebellion of the twelve districts it rules and exploits. Plus one. Involved in the rebellion are a handful of former Capitol citizens including one of the titular Deadly Game's best Gamemakers and a camera crew who use their skills to make rebel propaganda shots.
In Star Trek: Vanguard, the Tholians are under threat from Abusive Precursors (and Scary Dogmatic Aliens) the Shedai. Tholian officer Nezrene gets fed up with the Ruling Conclave’s inability to put aside their xenophobia and seek alliance with outsiders. She knows that to stand against the Shedai, Tholia requires the aid of its neighbours and should co-operate peacefully. She and Ezthene, who has come to a similar understanding, leave the Tholian Assembly as fugitives in order to join up with the Federation at Vanguard Station.
In the Belisarius Series, there's Kungas and his Kushan squad, another group of Kushan troops captured by Belisarius, and finally Damodara, Rana Sanga and his entire Rajput and Ye-tai army.
Captain Marko Ramius in The Hunt for Red October had become disgusted with the USSR's political system, as his wife died from a botched medical procedure, and the physician was not reprimanded because he was the relative of a ranking Party member. He was also disturbed by the destructive potential of the titular ship, "a ship which had but one use", as he puts it.
In the Star Trek Mirror Universe story "The Mirror-Scaled Serpent", mirror!Seska is a member of the Terran Rebellion and fervent in her disapproval of the Alliance. She believes the Cardassians should rule the quadrant, but they shouldn't have have allied with Klingons to do it.
In Poul Anderson's "A World Called Maanerek", Horlam. He admits that in watching for deviance, he had not been watched himself.
In the short story "The Ones Who Walk Away from Omelas" by Ursula K. Le Guin, it's mentioned that there are people who will simply leave the utopian city without a word, ostensibly due to the child the city keeps locked away in a basement with virtually no outside interaction except when given small amounts of food, because it is believed that once the child is shown kindness, their society will fall apart.
Firebird: Firebird, who requested asylum from the Federacy as protest against her homeworld of Netaia killing massive amounts of Verohan civilians and rendering Veroh uninhabitable.
Crown of Fire: Terza Shirak, who left the Shuhr primarily to save the life of her daughter, but also because she had never fully agreed with their callousness towards human life.
In the MYST books, Atrus and his group happen across Terahnee, a land of seemingly infinite plenty, led by wise descendants of the survivors of the fall of D'ni. One such descendant, though, owing to the kindness shown him by the invisible, horrifically-treated underclasses when he grew sick, eventually leads the first steps towards a rebellion.
Live Action TV
Gaheris Rhade in Andromeda's "The Unconquerable Man" begins the episode by betraying the All Systems Commonwealth to help his people attempt a conquest, but then spends the next several years trying to restore the Commonwealth once he sees that his people are too self-centered and obsessed with in-fighting to really make a go of a galactic empire.
Rhade is a double example; the reason he originally betrayed the Commonwealth to the Nietzscheans is because he believed the Commonwealth's treaty with the Magog showed that the Commonwealth was too weak and decadent to defend its people.
Said treaty also handed over a number of Nietzschean worlds to the Magog. They were not happy.
Telemachus Rhade (the genetic reincarnation of his ancestor Gaheris for bonus points) is essentially the living embodiment of this trope.
Riley Finn. He was initially completely loyal to the Initiative, but as he uncovered more and more of its corruption, particularly after Professor Walsh attempted to kill Buffy in a Death Trap, he began to desire to leave. When the Initiative captured Oz, a werewolf, and conducted inhumane experiments on him even after he reverted to human form, that was the straw that broke the camel's back; he promptly turned his back on them in favor of the Scoobies and helped Buffy and co. break Oz out.
Buffy never really cares about what the Watchers' Council has to say about how she does things. During season 3, she gets particularly disgusted when their Cruciamentum test results in the Ax-Crazy vampire they captured to test her breaks loose and kidnaps her mom, and when they refuse to help her save Angel after he is poisoned simply for being a vampire, that was the straw that broke the camel's back.
Worf in Star Trek: The Next Generation and Star Trek: Deep Space Nine might be an aversion — while he makes himself an exemplar of how he views Klingon honor, he never turns on the Klingon race for not living up to his romantic views. (He's not above some kingmaking (twice!) for the good of the Empire.)
The Next Generation episode "Face of the Enemy" features a character who plays this trope straight-up twice (the second time, he realized the grass wasn't so green on the other side after all and defected back).
In the Next Generation episode "The Defector", there's a subversion. A Romulan admiral defects to the Federation because he has become disgusted with his fellow Romulans' warlike ways. It turns out the special information he was offering Starfleet was false. The Romulan Empire wanted to trick Starfleet into taking an aggressive stance against them, and they wanted to test the Admiral's loyalty, all part of an elaborate plan. The Enterprise narrowly escapes, but the Admiral, despondent to learn his "defection" was all in vain, kills himself.
What Garak becomes after Dukat invites the Dominion to take control of Cardassia. Believing the Dominion does not have Cardassia's best interests at heart, he throws in his lot with the Federation and combines efforts with Kira and Damar to organise La Résistance. He knows it will destroy the Cardassia he loves (although even he was shocked by just how thoroughly the old Cardassia was destroyed) but he does it anyway.
Odo, despite not knowing his people until the third season, manages to pull this off well. His attitudes about law and order are shared by his people, but they built an empire based off this and keep trying to get him to defect throughout the show.
Teal'c has gone as far as killing himself from alternate worlds without batting an eye.
Tomin starts to doubt the Ori late in Season 10 and finally performs a Heel-Face Turn in "Ark of Truth".
In Doctor Who, the Doctor might have left his home planet, Gallifrey, for this reason. The page quote shows that even if he hadn't, he should have. Portrayals of the Time Lords have differed quite a lot Depending on the Writer but all the early portrayals showed a Sterile Crystal Spires and Togas society that had decided not to interfere with the universe. Later portrayals (like The Deadly Assassin) showed/Retconned Gallifrey into a decadent Crapsack World ruled by an arrogant elite. The Invasion of Time even showed that a band of defectors lived in a BBC Quarry just outside the Time Lords' Citadel.
In The End of Time, the Doctor flat-out admits that he chooses to remember all that was good about his people and tries to ignore all the terrible, terrible things the Time Lords did - and plotted to do - when they went to war with the Daleks. When Rassilon and his followers almost escape the Time War with a plan to rip apart the Time Vortex itself and achieve godhood, the poor Doctor is forced to face just how fatally flawed his kind were once again.
Delenn broke the Grey Council in Babylon 5 after it became apparent they would not join the upcoming Shadow War.
Only a partial example. She never defected from Minbariness(except biologically which she assumed to be in the Minbari people's interest by promoting cooperation). Nor did she renounce her high prestige at home.
Captain Sheridan and his officers seceding from Earth.
Kosh turning against the rest of the Vorlons.
Vir Cotto working in secret to protect Narn refugees during the Centauri occupation, along with his general spoken distaste for the decadence, power games, and atrocities associated with the Centauri Republic at the time, and the influence of the Shadows (and concern for Londo for getting caught up in all this).
Played with in Farscape, in which Chiana is a Defector To Decadence. Most of her culture, the Nebari, are repressive, puritanical authoritarians, while she is abitdifferent.
Aeryn Sun does this trope in an interesting way: her throwing in her lot with Moya's crew was involuntary (the Peacekeepers were going to kill her as having been irreversibly corrupted), but after having John's humanity rub off on her she begins to see all of the cruelty and horribleness of the Peacekeeper way of life, and by the time she's around Peacekeepers again it's clear she no longer agrees with them in the slightest.
Joe from Kaizoku Sentai Gokaiger was originally an elite within the Space Empire Zangyack before he left to become GokaiBlue after his superior order him kill innocent children. Joe's senior officer and close friend, Sid Barmick also does this after the incident above and was the one who encourage him to get away from Zangyack. Too bad for him He was captured and turn into Barizorg, his memories were erased and programmed to serve only the emperor and his son.
The Mole Beastman from Kamen Rider Amazon decided to pull a Heel-Face Turn because his old bosses are firm supporters of You Have Failed Me and pretty much his only options with them were A) be brutally torn to shreds by Amazon or B) return to base and die horribly at the hands of the Big Bad. What clinched it was that Amazon actually took pity on him and saved him from execution, convincing him being a good guy was the better choice.
First Wave has Joshua, one of the key Gua military leaders. However, in his first appearance, he reveals that he seriously doubts his people's chance of success despite their advanced technology and the ease with which Gua operatives are able to infiltrate humanity. One episode consisting mostly of flashbacks involves a Gua council deciding whether or not to start the Alien Invasion. Joshua is the only one arguing against it, claiming that, if every 117th human is The Determinator like Cade Foster (the protagonist), the invasion is doomed to fail or, at best, to be a Pyrrhic Victory. He also reveals that his people used to be peaceful until another race conquered them. They toughed up, threw off their oppressors, appropriated their technology, and named themselves "Gua" ("power to overcome" in their language).
Charmed: Billie thought she was this when Christy turned her against the Charmed Ones.
A fairly common method both for bringing about a Heel-Face Turn and breaking up a villainous stable.
The most famous of these defectors was arguably Batista. For more than two years, he was The Brute in Evolution, a faction on Monday Night Raw that also consisted of Hunter Hearst Helmsley (a.k.a. Triple H), Ric Flair, and Randy Orton. After Orton was expelled from the group in the summer of 2004, however, Batista began to have second thoughts about being a member of Evolution. He kept a low profile at first, though, ostensibly remaining an ally of Helmsley and Flair while privately expressing disgust at their methods. It wasn't until he won the Royal Rumble Match in January 2005 and was presented with an opportunity to challenge Helmsley for his World Heavyweight Championship that Batista realized that the moment for defection had come. After pretending to sign a contract that would have moved him to SmackDown! to challenge John "Bradshaw" Layfield for the WWE Championship, Batista revealed that he would stay on Raw by powerbombing Triple H and challenging him for his championship at WrestleMania. This marked Batista's official exit from Evolution - and the beginning of his highly successful singles career.
And, in a reverse example in TNA, Flair himself turned his back on his group Fortune in early 2011 after the other members turned face and declared war on Hulk Hogan's faction, Immortal, with which Fortune had been closely affiliated up to that time; Flair officially declared his allegiance to Immortal, becoming a mentor to Matt Hardy.
Kelly Kelly (who wasn't really a heel, but was essentially acting as one at the time) experienced a similar change of heart in the summer of 2007 on ECW On SciFi. She had gained notoriety on the program over the past year with her "Extreme Expose," a combination dance/burlesque routine that definitely put the "Extreme" in ECW. Early in 2007, the act became a three-woman show when Layla El and Brooke Adams joined Kelly in her performances. The girls at first simply entertained the crowds in between matches, but soon they found themselves unofficial cheerleaders for The Miz, who had recently been drafted to the promotion from SmackDown! One night Miz's opponent was Balls Mahoney, and Kelly realized that she had become smitten with him. She began to show sympathy for Mahoney, as well as resentment toward The Miz and Layla and Brooke for bullying him. She tried to quit Extreme Expose (her own creation!) but quickly found out that she couldn't, because Miz owned all three girls' contracts. In the end, The Miz cut his ties with Extreme Expose to become John Morrison's tag-team partner, Brooke left WWE only to be reborn as "Miss Tessmacher" (Eric Bischoff's Sexy Secretary in TNA), and Kelly and Layla became bitter enemies for the rest of their stay in ECW and later on Smackdown.
The Craftworld Eldar and Exodites of Warhammer 40,000 are an example of this on a massive scale: millions of Eldar, disgusted by the unrestrained decadence, hedonism and perversion of the majority of their race, left their society, some to live aboard gigantic spacecraft called Craftworlds, some to live on unsettled wilderness planets. They now live painfully repressed lives, focusing their lives on one Path at a time while in constant denial of their baser urges. However, they turned out to have the right idea when the remaining Eldar's hedonism Squicked a Chaos god into existence, complete with star-eating Negative Space Wedgie and species-wide Mind Rape that pushed the Eldar to the brink of extinction.
Every now and then a Dark Eldar grows weary of the figurative and literal backstabbing, hedonism, and soul devouring villainy of his/her kind and joins a Craftworld.
There's buckets of this in World of Darkness games, both Old and New — largely due to the tendency for supernatural creatures/people to squabble amongst themselves like crazy. Prime examples include:
The Sons Of Ether/Technocracy split in Mage: The Ascension. Sons Of Ether are basically people who think that science should stay awesome, and the Technocracy wanted the Etherites to follow the instruction manual.
Both the Sabbat and the Anarchs in Vampire: The Masquerade started this way. And Adonai of the Salubri inverted the trope, breaking from the Salubri (who opted out of vampiric decadence altogether) and joining the Sabbat to get his revenge on the Tremere. The result was the Salubri antitribu.
The Werewolf: the Apocalypse story collection had a short story featuring a redeemed Black Spiral Dancer gone ronin.
Uktena (the totem spirit of the Uktena tribe) was once a servant of the original balance-Wyrm. When the Wyrm went insane, Uktena promptly defected to the Wyld.
In GurpsTraveller Interstellar Wars the populations of conquered Vilani worlds did this en masse. They felt little connection to the Vilani Imperium and some(like the Khimishargu Vilani) were even rebels. The Terran Confederation by contrast treated them well. Thus they borrowed Terran ideas, intermarried with Terrans and even fought for the Terran Confederation against the Imperium.
In Magic: The Gathering, Sorin Markov despises the other vampires of Innistrad because they take pleasure in killing and eating people. Worse, many of them treat it as an act of indulgence as opposed to survival. The rest of the vampires hate him in turn because he created the guardian angel Avacyn, the greatest obstacle in their conquest of the humans of Innistrad. Only a few of the vampires realize that Sorin did this for their sake too, since the overly indulgent vampires would drive humans to extinction if left unchecked (dooming the vampires to starvation).
In Rifts, Free Quebec defects from the Coalition States partly because they disagree with the Coalition's policies of enforced illiteracy, no free press, and entrenched bureaucracy (Free Quebec does have the last, they just like to pretend they have free elections). Interestingly, they also felt that the oppressive Coalition was too tolerant in other matters, such as mutant humans and psychics.
Not that she was entirely a part of the decadence to begin with, but Elphaba does this in Wicked; after dreaming of becoming an assistant to the Wizard for most of her life, she turns down the opportunity, along with the future of wealth, power and esteem that comes with it, because she finds out he was the one behind the very anti-Animal policies she had come to protest.
In Metal Gear Solid 3 Eva claims this trope as her reason for abandoning the United States and going over to the Soviets; when she became a code breaker for the NSA, she realized she'd been carefully manipulated by propaganda her entire life. This is a complete and utter lie, as we find out much later.
Similarly, The Boss claims that her main reason for defecting to the Soviet Union from her backstory was due to the decadence of her government. Despite this, the defection was still faked.
In the backstory of Devil May Cry, Sparda, one of the highest-placed leaders of the demons and himself the most powerful devil, turned against his own kind and saved humanity from extinction after he "woke up to justice." Many years later he would father the games' protagonist Dante and the Evil Twin Vergil.
Gorath from Betrayal at Krondor, though he's less a defector and more someone whom the self-destructive ways of his people compel to use methods to protect them that are seen as traitorous by most of his kind - except for those who share his views, but don't nearly have the guts to act on them.
Exemplified by Folka Albark of the Super Robot Wars series. Because he starts disagreeing with his race's way of life, he defects to the protagonist side and try to find out a new meaning of life for his race, which culminates into kicking the asses of his entire brethren.
Ralgha "Hobbes" nar Hhallas in Wing Commander. Hobbes was the Kilrathi pilot who joined the Terran Confederation (Human) side. Later it is revealed that he actually was a Manchurian Agent for the Kilrathi Empire.
In Ephraim's route we have the shaman Knoll joining Ephraim and his troupe for rather similar reasons, only he was slated for execution and the heroes found him before he was killed and after defeating the zombie!Emperor Vigarde.
Heath, from Blazing Sword, defects to your side after disobeying orders to slaughter innocent civilians. Legault is another of these, leaving the Black Fang (and looting its "base" at the Dragon's Gate in his way out) because he was sick of its continued fall in corruption and ruthlessness.
In Radiant Dawn, the player alternately plays with Micaiah's and Ike's army. Several members of Micaiah's army can join Ike's, depleting Micaiah's army of some of her much-needed decent units. While Jill's recruitment can only occur when the player makes Haar talk to her, Zihark can pull a Face-Heel Turnduring chapter 3-6, if he has a Bond Support with either Mordecai or Lethe (who are the bosses of this chapter, assuming they're still alive) and they manage to talk to him...
Prince Enrique of Valua, from Skies of Arcadia, is a literalDefector from Decadence. As his title states, he's next in line for the throne of the kingdom of Valua. He spends the early game an apparently minor NPC, telling his mother that crushing the poor, the weak, and the foreign under her heel just because she's in charge of an empire is just asking for trouble. The empress blows him off as young and idealistic, and remains cartoonishly convinced that unmitigated conquest is the only way to run an empire, even as it proves to be her downfall.
The Elites from Halo. In fact, according to the backstory the first Arbiter was this, leading to the position becoming a mark of shame for the Elites. The Elites later side with the UNSC when they finally realize the Prophets are massive assholes.
Canderous Ordo in Knights of the Old Republic abandons his mercenary ways and goes off adventuring with the player because he believes that the player will give him a chance to make the Mandalorians into a proud and honorable people again, instead of the mercenaries and thugs that now inhabit the galaxy.
In Fallout 3 there is a group that broke away from the Brotherhood of Steel because they believe that the leader has gone native, they call themselves the Brotherhood Outcasts. This came from the fact that the Brotherhood of Steel inside Fallout 3 is actually a part of the entire Brotherhood of Steel - their original mission was concerning advanced technology and preserving it, though the leader of the group became more heroic in his intentions and went out helping others, against the rather haughty technological-obsessions of the rest of the group. The Brotherhood Outcasts stayed loyal to their original mission.
In Fallout: New Vegas, it's possible for Veronica to decide to leave the Brotherhood and attempt to join the Followers of the Apocalypse once she's convinced that the Brotherhood are too set in their ways. This results in a group of Brotherhood Paladins wiping out a Followers outpost and attempting to kill Veronica for potentially spreading knowledge to outsiders.
A player pulled this massively in EVE Online. Having gotten tired of Band of Brother's "Stop Having Fun" Guys mentality, one of BoB's directors defected to Goonswarm, stealing over 20 billion in assets from BoB and dissolving the BoB alliance.
Sorcha does this in the last level of the Pyro campaign in Sacrifice. It doesn't do her any good.
The Night Elves of Warcraft are an odd example, in that the decadent ones (high/blood elves) are the defectors when they lost the civil war. Several blood elf NPCs themselves then demonstrate this trope as defecting from their decadent and power-mad society, most notably one researcher permanently exiled from the blood elves who now lives with the tauren in Thousand Needles.
Tassadar from Starcraft disobeys orders from the Conclave to completely obliterate the Terrans to stop the spread of the Zerg. He eventually comes to believe that the Conclave is too old, rigid, and arrogant to be able to rule the Protoss effectively.
Tyrael does this to the Angiris Council after a loud argument regarding his actions in the prequel (namely saving humanity from certain doom.) He strips off his armor and falls from the High Heavens to Sanctuary. He eventually rejoins them, though as a mortal.
Subverted with Kormac the Templar. He was taken in as a criminal by the Order, magically and physically tortured until his memories were repressed, and told he had been redeemed at their hands. This trope is set up when he finds out he was actually an honest soldier of Westmarch and the whole "redeemed criminal" stuff was a facade. However, he stays faithful to the order and vows to clean it of those responsible.
Deconstructed (?) with Kormac's former templar brother Jondar. He had a similar revelation at some point, but it left him heartbroken and in a mentally weakened state. Then he was discovered by, and persuaded to join, the demonic Coven.
Lyude from Baten Kaitos. First exiled to an embassy for speaking out against a planned massacre of a village controlled by The Empire, he defects to the hero party when the empire attacks the island he was sent to under false pretenses of protecting the empire from the other kingdom's non-existent imminent assault.
Until He goes back to The World That Never Was to try and kill Xemnas and free Kingdom Hearts. Before that gets anywhere, Riku beats the crap out of Roxas and drags him into the Twilight Town simulation to keep the nobody from getting himself killed.
Leonhardt, Agarest Senki's first generation protagonist is one of these - he switches sides to the more peaceful natives during an invasion when one of his fellow generals moves to kill a defenseless elven child.
Axl from Mega Man X 7 was this as well. He was originally a member of the Red Alert vigilante faction, but left the group, anticipating fully that they'll attempt to force him to return, and eventually defected to the Maverick Hunters, because they had changed for the worse. It's later revealed that the reason why they changed for the worse was because of Sigma, AKA The Professor.
Mish from Amea refuses to go through with a process that would do away with the pain and suffering in his life because it would turn him into a slave of the Master. He ends up payingverydearly for it.
Some of the Templars in Dragon Age II start questioning their loyalty as Meredith's measures grow more brutal. By the third act, there's a joint mage-templar conspiracy to oust her and get the Circle back on track. Unfortunately, one of them is more interested in revenge on the player character.
Messed with by Legion in Mass Effect 2. It at first looks like they are setting it up as a defector from the evil Geth civilization, until it reveals that it is actually part of the larger Geth civilization and the evil Geth are the defectors, or "heretics".
Later played straight in the Paragon ending when Miranda tenders her resignation to Cerberus (to the Illusive Man's face, if you bring her to the final boss).
Wrex in the first game, similar to Canderous above.
In Mass Effect 3, your war assets have a folder dedicated exclusively to "Ex-Cerberus" personnel disgusted with the Illusive Man's new tactics. Jacob can be found protecting a team of scientists who realized something was wrong when their colleagues began mysteriously disappearing. The Rebellion Pack makes "Cerberus Defectors" a whole multiplayer class.
Riven also broke away from Noxus after they used chemical weaponry to kill both the enemy regiment and her own instead of allowing them to face in battle so the stronger army would come out victorious.
Player character Yuri in Modern Warfare 3 used to be a close friend and comrade of Makarov, the world's greatest terrorist. He started having second thoughts as the Ultranationalists became increasingly insane. Came to a head right before the infamous "No Russian" mission — he tried to stop the massacre and Makarov shot him in the gut for it. He's now the only person in the world who hates Makarov more than Price.
Makarov is something of an inversion. He left the other Ultranationalists and formed his own group, because the others weren't decadent enough.
The backstory of the Myst games, particularly the tie-in novel The Book of D'ni, reveals that the entire D'ni race is one of these. When their original homeworld was dying, most of the population moved to the Age of Tehranee, a decadent world of perfect climate and boundless space. A small part of them, however, went to another world, D'ni (or Earth), where they would live underground and be forced to eke out a living through advanced engineering abilities. The purpose of this was, similar to the Amish movement, to prevent decadence from rotting society, and it failed: the exact same kind of sedentarity and elitism that plagued Tehranee also crept into D'ni society, and ultimately caused the downfall of both civilizations. At some time in the series of the games, Atrus builds a new Age, Releeshahn, for the D'ni survivors, and founds a new society meant to address these issues by introducing such policies as social equality.
Whether Abysswalker Artorias is this or a Fallen Hero is the subject of much debate in Dark Souls. Artorias was one of Lord Gwyn's four great knights, making him one of his top lieutenants, and one of the most important character in his court that isn't an outright god. An unknown number of years ago, the Darkwraiths (Humanity devouring dark knights of the Abyss) appeared. They were so dangerous that it eventually resulted in outright sacrificing an entire city. Artorias was charged with hunting the Darkwraiths, but instead joined them for reasons that are not known. He died sometime after, also for unknown reasons.
Villainous example in Max Payne 3, where supplementary material reveals that paramilitary leader Neves used to be a cop but quit because he wasn't making a difference against the criminals.
Secret of Keychain of Creation is a deathknight gone rogue... sorta. She's restricted but has found ways of getting round it. Vulnerable to the occasional resonance blowout however.
Gamzee, if you think about it. He's of the highest blood colors, but all he wants is to be friends with everyone and relax with a pie.
Lien Lei of E-Depth Angel hated his father (and the rest of his family) so much, that although he was still in charge of part of his father's company, he didn't care about getting approval for anything. This is part of what allowed him to finally go along with Angel's plan to "save the cyborgs' humanity". He even devoted large amounts of funding toward it, though his devotion for the program may have been for totally different reasons.
In The Gamers Alliance, Omaroch wants do something else with his life than just randomly kill people like other demons do. This leads him to enter the Land of the Living and he eventually falls in love with a human cleric, leaving his old life behind and siding with humans against his kin.
Flapper Jack's special talent is protecting ponies.... and the guard he's in grows increasingly corrupt and abusive.
Dark General Cobalt in Sailor Nothing, although he needed magical aid to get there.
MSF High Forums: (combined with Heel Face Turn) Casey's 'parents' are frequently mentioned as supervillians. Casey is looking forward to becoming a Super heroine and beating them and their allies down.
In Worm, following the events of Echidna, twenty or thirty superheroes leave the Protectorate altogether, realizing that it is controlled by a Nebulous Evil Organization. This is inverted by the Villain Protagonist, who subsequently joins the Protectorate in hopes of keeping it afloat.
Dinobot from Transformers: Beast Wars thought Megatron stranded him on an abandoned planet and defected in the first episode. In the second season, after realzing everything was going according to Megatron's plan, Dinobot returned to Megatron's side... Only to defect again once he realized what the full scope of Megatron's ambitions really was.
Skyfire from the Original Series was revived after being frozen in the Arctic and joined the Decepticons, not because he knew who they were, but because his best friend was one... Then he realized his best friend had become evil since he was frozen. Oops.
More to the point, his best friend was Starscream, which raises questions in and of itself. Then again, this was several million years ago back in the days Starscream was a scientist.
Starscream attempts to do it in Transformers Prime too, but this is scuppered by Arcee trying to murder him and make it look like she killed him as he was attempting to escape custody.
Blitzwing does this in the five-part Season 3 opener of the Transformers Generation 1 series, after seeing his fellow Decepticons manipulated by the Quintessons and how psychotic Megatron had become as Galvatron.
Marsala in Exo Squad, A Neosapien who fought for the Exofleet against the second Neosapien rebellion, which he must have really disagreed with, because he was one of the leaders of the first one.
He even goes on a Motive Rant when they thought he switched sides on his views about how humans treat Neosapiens. It turns out all of it was true, but he still believes the two races can get along, plus the second rebellion is committing genocide.
Inverted by Shego, Dragon to the Mad Scientist main villain from Kim Possible, who actually used to be a super hero before she got sick of all the relentless smiling and cheezy good deeds. By all accounts, she is much happier as a Dark Action Girl.
Well that and her annoying siblings as well. Though she does still care about them.
Zuko, from Avatar: The Last Airbender , finally decides to officially defect from the Fire Nation after witnessing his father plan to burn the Earth Kingdom during Sozin's Comet.
Jeong Jeong, after seeing what the Fire Nation had become.
Several characters from Motorcity, including Mike, a former cadet to the show's Big Bad, his La Résistance members Dutch and Julie (though partial in her case given that she's the aforementioned Big Bad's daughter and acts as a insider), and Jacob, formerly a renowned scientist. All, along with many possible others, escaped the dictatorship of Detroit Deluxe to the city below: the original, but much grimier Motor City.
Lemongrab 2 from Adventure Time. By the time of the episode "Too Old", the original Lemongrab had become mad (well, madder) with power, putting Shock Collars on the Lemon Children and almost eating his brother alive. When Lemongrab imprisons Finn and Bubblegum for wanting to take Lemonhope (the most normal of the Lemon Children) to Candy Kingdom for education, Lemongrab 2 starts rebelling, first by freeing them, then by releasing the Lemon Children from their collars. Before Lemongrab finishes eating him, Lemongrab 2 asks Lemonhope to go with Bubblegum and become successful for the sake of the other Lemon Children.
President John Tyler switched from the Democratic party to the Whig party because he didn't like Andrew Jackson's dictatorial methods. The switch wasn't successful because he remained just Democratic enough that most Whigs couldn't stand him.
Missing records and contradictory stories make it hard to tell how much this applied to history, but legendary samurai Yagyu Jubei is often portrayed as a Proud Warrior who spent years Walking the Earth after being banished due to his disdain for court politics and blunt ways.
Democratic senator Stephen Douglas was, for a time, considered as a possible candidate for the Republican nomination for president in 1860 when he defied his party and fellow Democrat President James Buchanan over their attempts to pass a slave code that would have made Kansas a slave state regardless of whether the people wished it to be a slave or free state. For all intents and purposes Douglas' near defection split the Democratic party's northern and southern wings as Douglas would become one of two Democratic candidates for President in 1860, (the other being John Breckenridge) with Douglas getting nearly all of his support from the Northern Democrats. For their part, the Republicans wound up picking some obscure former Congressman named Abraham Lincoln instead, who, due to the split among Democrats, was able to win with just 40% of the popular vote. (Although, since it was a four way race, 40% was quite a bit more than Lincoln's nearest rival). After Lincoln's election, Douglas urged the South to accept Lincoln and attempted to work to avoid The American Civil War. When the South did secede, he condemned the action and rallied support for the North, but died not long after the war's onset.
Lincoln was not exactly obscure - he was the Republican challenger for Douglas's Senate seat in 1858, and although he didn't win, his famous debates with Douglas made him well-known among Republicans, although not considered a contender for the Republican nomination until he was nominated.
Many real-life defectors from communist nation-states were the elite of society. , , 
That's due to the fact that they (and "elites" is a strange word to use here, but I think I get what you mean) were the ones allowed to travel outside the country. You needed permission to even travel inside the country, to various degrees in different countries and regions of countries. There were sometimes army checkpoints and barbed electrified (to signal the nearest army outpost) fences even inside the country, not only around the borders. And also the fact that it's only to them that the term "defect" would make sense. If you had been given permission to leave the country for some reason, you were by definition of the "elites". If you managed to flee by not getting shot by the army patrols along the borders (there was a shoot to kill policy, and soldiers were given extra home leave for each refugee shot) that would be an escape, not a "defection".
The industrialist Fritz Thyssen was originally an ardent supporter of Hitler and the Nazi Party, up until he was thoroughly disgusted by Kristallnacht. He literally defected from Germany, causing Hitler to personally declare him an Un-Person, and holed up in France... until France was overrun in World War II. He was thrown into a concentration camp, but still managed to survive the war.
This seemed to happen a lot with the Nazis, maybe why there were 27 or so attempts on Hitler's life between '34 and '44, not including 10 or so in '33, and another 4 before that.
Saint Patrick's Battalion in the Mexican-American war, a majority-Catholic group of soldiers who defected from the US Army to side with Mexico. Reasons for the defection vary, but most of them fall under this trope: many were Catholics/immigrants embittered by mistreatment and cultural alienation from the largely Protestant/nativist American forces, many were Irish soldiers who saw America as doing the same thing to Mexico that England had done to Ireland, and some were escaped black slaves who were understandably disenchanted with the United States.
Similarly, many of the Irish rebellions against British rule saw Irish Catholic soldiers defecting to join the rebels. By the Irish War of Independence, this had come to include English and Scottish Catholics of Irish descent.
A really bizarre one was the Fenian raids, in which Irishmen based in the United States attacked British forts in Canada, which Washington supposedly ignored because they were still angry with Britain for toying with backing the Confederacy in the late unpleasantness.
And the Connaught Rangers, an all-Irish regiment of soldiers serving the British Empire in India, defected almost immediately upon hearing news of the Irish War of Independence. Moral of the story - do not piss off the Irish.
Street gangs see a lot of abandonment from their founding 'OGs' due to the shift in values (many gangs are started for neighborhood protection but then the drug trade becomes too lucrative, leading the gangs to become more like criminal enterprises). Many founding members feel like the new generation doesn't have the respect and focus that they have and can no longer tolerate it.
Two of the most prominent anarchist theorists Mikhail Bakunin and Pyotr Kropotkin were Russian princes, but rejected their privileged positions. Both ended up in prison at some time and later fled/were expelled into exile.
Leo Tolstoy, as well, although he didn't end up going to prison (and he was a count rather than a prince). The Russians seem to have a long and pronounced tradition of Russian nobles becoming anarchists and giving up their titles and possessions.
In the 19th and 20th centuries it was the Russian nobility, and not the Russian middle-classes or industrial workers, that made up most of the country's political radicals and dissidents. The Russian middle class was both weak and tiny, due to the power of the (state-run) companies they worked for, and big-factory workers weren't much more numerous or better organised by comparison (cottage industry, and small-factory-based-light-industry, employed most of the workers in even the 1913 manufacturing sector). That said, most of said radicals and dissidents came from the less well-off or impoverished echelons of the nobility.
Another Tolstoy example might be Count Aleksey Nikolaevich Tolstoy, a distant relative of Leo Tolstoy. He fled Russia after the Revolution, but embraced communism and returned to Soviet Union where he became one of Stalin's favorite authors and made major contributions to early science fiction.
Louis Philippe, the Duke of Orleans. He became a major supporter for the revolutionary causes during the French Revolution and changed his name to Citizen Equality (Citoyen Egalite), abandoning his aristocratic status. Unfortunately for him, things did not go well for him during the Terror.