"With kindness comes naïveté. Courage becomes foolhardiness. And dedication has no reward. If you can't accept any of that, you are not fit to be a magical girl."
Goku of Dragon Ball is this full throttle. Throughout the series he is constantly offering his opponents a chance to change and be good people, even after they kill his friends he still has hope for them. He is overwhelmingly optimistic and nice to every person he meets. This will not, however, stop him from fighting to protect the people he loves.
Except his intro speech at the end of the first chapter goes, "no, swordsmanship is an art of killing. Kaoru-dono believes a sweet, naive lie. But if this one had a wish...it would be that her sweet lie would become the truth of this world." Kenshin's Walking the Earth with Obfuscating Stupidity routine involves some serious ideals, but despite avoiding his battle expression most of the time he's not too wide-eyed. He's got the world-weary thing going, but values Kaoru as a Wide-Eyed Idealist.
Some of the stupidity probably isn't fake. The line is impossible to find, as is common with Crouching Moron, Hidden Badass types.
His backstory involves a bit of this, despite all his childhood trauma—it caused him to wind up a sworn assassin in a civil war.
Touta Matsuda from Death Note. Deconstructed with Light: it's pointed out that he is "quite the positive thinker" and ironically it's his idealism that drives him to commit his atrocities in order to "make the world a better place."
Kanzaki Nao in Liar Game. Almost every chapter. You'd think that one of these days she'd learn...
Except you know, she's usually proven right by the end.
Ichiro Yamada from the manga Freesia. He very much initially thinks that he can help the country by punishing ex-convicts and such, until he realizes quickly that the Vengeance Proxy Enforcer firm that he works for is nothing more than a group of contract killers for people who have massive grudges.
Both Suzaku Kururugi and Princess Euphemia Li Britannia from Code Geass genuinely believe they'll be able to reform the shockingly racist Britannian Empire and be facilitators for the peaceful integration of the Japanese people into the empire's fold. Cue Diabolus ex Machina on a national scale.
This is subverted in the second season, where Suzaku forms a reasonable, if rather myopic, plan to free Japan (the rest of the world isn't his concern) and begins suffering from a bad case of Motive Decay until he realizes his ideals are nothing but smoke.
This is spoofed in official side comics, where Suzaku and Euphy are portrayed as so blindingly naive that they still believe in the Delivery Stork and Cabbage Patch Babies, while Lelouch looks on in stunned disbelief.
This trope is lampshaded artistically with Shirley, who has literally the largest eyes in the whole cast, with Euphemia just in second place.
In the manga version of Fullmetal Alchemist Scar's brother and the Rockbell family are wide-eyed idealists who believe in the basic good nature of man. The Rockbells leave their practice so they can heal the Ishvalans being massacred by the Amestris army, and Scar's brother wants to learn alchemy so that he can better understand the bonds of humanity. During an attack Scar's family is killed, and Scar's brother tries to shield Scar, but is unsuccessful, and Scar loses his arm, Scar's brother sacrifices an arm and his life to save Scar, and Scar wakes up in the Rockbell's hospital. Finding out that his brother's arm is now attached to him causes Scar to go temporarily insane, and he kills the Rockbells in a Freak Out.
Roy Mustang is the other side of the coin. His sometimes borderline dumb faith in human nature helps him sometimes (when he took for granted Dr Knox would cover his scheme to save Maria Ross, because they were war buddies) and other times dooms him (when he believed overthrowing the Fuhrer would be a piece of cake when people found out he was a Homunculus. It turned out the brass knew and couldn't care less). Still, his idealism is precisely what makes his subordinates so loyal to him.
Havoc: He's stupid! How can such a naive thing keep climbing up in this country?
Hawkeye: I think it's good that there are idiots like that, once in a while.
The first anime, on the other hand, makes a point of contrasting Al's childlike optimism and naivete with Ed's growing cynicism and the horrible truths of the world aroung them.
Ai Tanabe, the newest member of Section 7 in Planetes. Her first name means "love," and it just picks up from there. She's taken to task for it countless times by fellow Section 7 crewman Hachimaki and Claire, Hachi's former Love Interest, the latter of which causes her to doubt her own ideals. And yet, although she's set up for a particularly cruel Diabolus ex Machina, which she could avoid by betraying her convictions, she stands by them to the absolute, heart-wrenching end, to Claire's shock. Given the nature of the series, she's proven right at the end.
Yuna Kagurazaka is one of the rare examples of this trope not to suffer either of the standard fates.
This is what makes Alice L. Malvin of Pumpkin Scissors stand out from many of the other nobles of the setting. She firmly believes in her cause to "eradicate evil" and that others will push for it too. This is what got Machis and Oland to join in the first place.
Albert from Gankutsuou, along with having Horrible Judge of Character. He is undoubtedly the most naive and idealistic of all the characters in that series. He truly believed for a long time that his friends' (and his own) families were perfectly rosy, and that the Count is a wonderful person. (He was very wrong, by the way - they were all insanely messed up.) Not to mention how he manages to go on about "true love". However, despite all hardships he goes through, Albert ends up taking the route A and becomes a better person who not only saves the Count's soul from Gankutsuou but also fixes his father's wrongs by becoming an envoy of peace.
Negi of Mahou Sensei Negima! starts out as one of these, but he eventually starts to realize that good and bad aren't quite as clear cut as he thought they were. Evangeline actually deliberately discourages his idealism (despite the fact that she's a Noble Demon who's constantly sliding towards Anti-Villain territory). Negi eventually admits that he can't always be the good guy, although he still tries to go with most "good" option available
Tenma and Nina from Monster, despite being frequently subjected to horrific trauma. The fact that Tenma in particular absolutely refuses to become cynical about the human race drops him straight into Badass Pacifist territory.
Arguably, Éclair from Kiddy Grade, who, despite having dealt with the dreadful realities of GOTT and galatic politics for many, many years, has somehow avoided becoming a cynic, and actually keeps up her spirit to fight for her ideals. Granted, this may be due to two things: (1) she does use autohypnotic suggestions to block out some of her memories temporarily, and (2) as a superhero, and with her partner, she does in fact have the ability to back up those ideals with with force.
Akari from ARIA is a special case, in that she manages to stand out in a setting that is practically paradise incarnated.
Kafuka takes this trope and runs with it. Everything has a good side to her: a Trash Can is a 'Treasure Chest for the Homeless' and it only gets worse from there.
Trigun's Vash The Stampede is determined to be one. No matter what he sees, what humans or Knives or anybody do, to him or anyone. His traumas are simultaneously cases of Break the Cutie and Break the Badass, and are usually horrific. Worse in the manga, where he is clearly fighting to maintain his idealism over his own common sense and has a lot more bleak moments. The setting is also much darker, since the series went seinen after the Fifth Moon. But he always stands up again. Because he won't give up on humanity and by extension Rem.
And on himself. After all, if he gives up on people then what does he have to resist Knives' Hannibal Lectures with, and what have all these years meant? Therefore, Technical Pacifist willing to Turn The Other Cheek to a sometimes absurd degree.
The anime incident with Zazie mirrors Wolfwood's manga shooting of Rai-dei, in both cases to protect Vash. Vash is not appreciative, because he feels his sworn enemies should always have another chance to not-shoot him. Wolfwood, who's got a certain Knight in Sour Armor and Anti-Hero thing going on, thinks he's crazy but wishes he could believe the way Vash does.
Wolfwood's a priest. There are intentional religious themes here, although they are way vague and have a distinct lack of real theology.
Vash is helped by his own awesomeness; when Knives and his subordinated aren't involved he can usually pull a casualty-free resolution out of the worst situations imaginable. Sure, this has meant horrific scars all over his body, but it gives him all kinds of warm fuzzies and hope. He wants Wolfwood to see this. Wolfwood wants him to see that most people are only human and you can't save everybody all the time.
When Vash has a Heroic BSOD it's usually because of this getting challenged harder than usual. On some level he disbelieves a lot of it, and the fact that it's sheer will keeping him in line sometimes distinguishes him from the kind that are this because they don't know better. But somehow he keeps regaining Incorruptible Pure Pureness.
Know who's the Trigun poster child for this trope? Manga Knives. He was all "our hearts are the same as people's, I'm sure if we try we can understand one another," and actually cried when the first human they met besides Rem accepted them. Then he Went Mad From The Revelation that Humans Are Bastards, and resolved to Kill 'Em All.
Meryl is a little naive but never an idealist. Millie is...strange. Maybe a wide-eyed idealist. Maybe just terminally clueless. Actually very sharp under it all, and very tough.
Anime Millie is Wolfwood's other foil, and they become a couple. One of Wolfwood's Character Development soliloquies involves the frustrated observation that Millie and Vash always "do everything I can't, like it's no big deal."
UC Gundam, have at least one pacifist who thinks they could stop the fighting, usually they are proven wrong and lives to watch the ramifications of their actions.
The titular character of Revolutionary Girl Utena, which, for some, can be infuriating when you realize that she refuses to see the emotional hardships that her peers go through (Juri's conflict over Shiori and her sexuality in general come to mind; Utena brushes it off and tells her to stop acting cold). Miki is this to a lesser extent, in regards to his sister Kozue, but it may be more that he's a genuine Nice Guy more than anything else.
The anime and manga incarnations of Princess Amelia of Slayers, both genuinely and to a comedic extent. She does have a blind eye towards the more wicked intentions of certain foes, especially the Monster race, but this is more of an ideology taught to her than anything else because of her violent family history. In the novels, where she's more mature, she's still optimistic, but her idealism falls more into Stepford Smiler territory.
The anime-exclusive character Filia, the Golden Dragon, is this combined with Holier Than Thou taken to aggravating levels. It doesn't help that she was sheltered for most of her life, but even after she learning the Awful Truth, during the last battle she believes that the Big Bad isn't beyond salvation (it's established clearly that he is at that point) and doesn't want to destroy him, even as he's consuming the world at that moment...
The neo-nazi band in Black Lagoon. Having no real experience with the way the criminal underworld works they're sent on a fixed race to "test their ability" against the protagonists, where they overspend resources, repeatedly underestimate the crew of the Lagoon, refuse to see facts, and waste time making dramatic and hammy proclamations about their heroic destiny as champions of the white race. Revy and Dutch kill all of them, and their would-be patron abandons them the moment it's obvious to him they've failed (though not before admitting to the leader that he set them up in the first place).
Rock also struggles with this in earlier arcs: His attempts to understand Revy makes her angry at him, trying to 'save' Gretel failed utterly, and his attempt towards Yukiko backfires completely. It isn't until "Le Baile de la Muerte" he starts to understand that if he wants to save people he'll have to become a cynical rotten power-player like Chang and Balalaika.
Comicbooks
Steve in Gilbert Hernandez's "Love and Rockets X" story within Love and Rockets.
Tomcat in the Jedi vs. Sith. He believes everything he hears in the songs and stories that claim the Jedi are invincible heroes. When he ends up in the middle of the battle against the Sith and sees Jedi dying in the mud with their non-Force sensitive comrades, it does not end well.
In Mr. Smith Goes To Washington, all Mr. Smith wants is a Boy Scout camp and nature preserve on a piece of land. Too bad the rest of the Senate is against him.
While Charles Xavier in X-Men: First Class isn't exactly naive, he still has an extremely idealistic attitude towards Mutant/Human relations. Even when the humans turn on the X-Men in fear, he still continues to beieve that the mutants should try to be the better men, in the hope that they will someday be accepted.
Otto from One, Two, Three about Communism. He even thinks it's a capitalist lie that Siberia is cold, and is happy that the Communists assigned them "a magnificent apartment, just a short walk from the bathroom!"
Literature
Sansa Stark from A Song of Ice and Fire, who bases her whole life around singers' tales, is a perfect little lady, gentle and trusting. Until the person she is starry-eyed over cuts off her father's head in front of her.And then MUCH misfortune followed.
Subverted by Carrot Ironfoundersson. He starts out as a wide-eyed idealist... Except that for some reason, his idealism somehow works. He can talk anyone into behaving like a friendly, reasonable person. If any other character tried it, they'd be dead.
It works because he's big, strong, usually accompanied by city watchmen (including a troll and later a golem) and, most important of all, is fairly intelligent. Carrot is an actual idealist, rather than just naive like most of the examples here; he knows full well that Humans Are Bastards and simply refuses to be one himself.
True but the world does tend to warp itself around him. After all he may or may not be the heir to the throne of Ankh Morpork and in a world chock full of narrativium, how can things not go his way.
Well almost any other character. In The Colour of Magic and The Light Fantastic, Twoflower, if anything, has an even more rose tinted view of the world, to the endless irritation of his traveling companion Rincewind - and likewise comes to no harm. Admittedly, this is probably because he travels with a Cosmic Plaything, so all of the trouble they run into goes goes after Rincewind rather than him. After they part ways, he does get thrown in a dungeon to rot for being so wide-eyed, which supports that theory.
Moomin- 'all I want is to grow potatoes and live in peace'-troll of The Moomins
Jane Bennet of Jane Austen's Pride and Prejudice. Her younger, more cynical sister, Elizabeth, is convinced that Jane's new friend, Caroline Bingley, deliberately sabotaged her romance with Caroline's brother in order to hook him up with his best friend's sister — all to increase her own chance of getting hitched to said best friend. Jane remains convinced that Caroline is her affectionate friend and would never do anything to hurt anyone, and more importantly, never do anything less than beneficial to her brother's happiness. Obviously he must prefer Georgiana... It takes a surprise face-to-face meeting with Caroline for Jane to admit Elizabeth was right about her, but she displays the same naivete and belief in love and the innate goodness of man when Wickham seduces their youngest sister, Lydia—despite Jane and Elizabeth knowing that he's tried the same technique on at least two other girls.
Voltaire's Candide. Among many, many other examples in the book is Dr. Pangloss's thoughts on having caught syphilis, and having had an eye and an ear removed as part of the treatment:
"O sage Pangloss," cried Candide, "what a strange genealogy is this! Is not the devil the root of it?" "Not at all," replied the great man, "it was a thing unavoidable, a necessary ingredient in the best of worlds; for if Columbus had not caught in an island in America this disease, which contaminates the source of generation, and frequently impedes propagation itself, and is evidently opposed to the great end of nature, we should have had neither chocolate nor cochineal."
Colin Creevey in Harry Potter falls under this with his cheerful, naive, and innocent loyalty to Harry at all costs.
Hermione also has her moments, with her working for House Elf rights even though they have Happiness in Slavery, much to the amusement of others who know better.
In Outbound Flight, the smuggler Maris Ferasi fit this trope pretty well. She had the utmost trust in and adoration for the Chiss commander Thrawn. Unusually, she wasn't disillusioned within the book - Thrawn lied about what he had done to resolve an extraordinarily prickly conflict, letting her leave without knowing just how much of a Downer Ending the whole issue became. Why?
Thrawn: There are all too few idealists in this universe, Car'das. Too few people who strive always to see only the good in others. I wouldn't want to be responsible for crushing even one of them.
Car'das: And besides, you rather liked all that unquestioning adulation coming your way?
Thrawn: All beings appreciate such admiration.
Drizzt Do'Urden in Homeland; he gets mildly bitter during the later portion of the novel when he finds out that his favorite mentor Zak kills clerics by the dozens, not that he always enjoys it....
The young baby-faced soldier boy in All Quiet on the Western Front definitely qualifies. as should be completely obvious given the nature of the book and this page, he dies.
God-King Susebron from Warbreaker - his entire experience of life outside his palace consists of having been read a book of fairy tales by his mother as a child. Semi-subverted in that while he does develop a more realistic view of the world, he never loses his almost childlike sense of straightforward goodness.
I'd say Toglio in Norman Mailer's The Naked and the Dead. Always thinking to himself about how he and his squad are "The good ol' boys", hard-working and patriotic. Then, of course, he gets his leg shot up to hell and sent home.
Cosima from Comrade Death. She flat out refuses to see Sarek for what he really is. He confesses to abandoning her husband to die, and later refuses to save her grandson from going to war, and both times she dismisses his spite as being concealed guilt and claims he would have helped if it had been in his power to do so.
"Alone of us all, Rinaldo has no personal ambition. He sees in Conan a red-handed, rough-footed barbarian who came out of the north to plunder a civilized land. He idealizes the king whom Conan killed to get the crown, remembering only that he occasionally patronized the arts, and forgetting the evils of his reign, and he is making the people forget. Already they openly sing The Lament for the King in which Rinaldo lauds the sainted villain and denounces Conan as 'that black-hearted savage from the abyss.' Conan laughs, but the people snarl." "Why does he hate Conan?" "Poets always hate those in power. To them perfection is always just behind the last corner, or beyond the next. They escape the present in dreams of the past and future. Rinaldo is a flaming torch of idealism, rising, as he thinks, to overthrow a tyrant and liberate the people."
Zoe in Saving Zoë, and this trait is why her sister Echo believes she was killed by a serial killer who pretended to be a modeling agent.
Isherwood Williams in Earth Abides, although he's not a complete naif.
Twenty Thousand Leagues Under the Sea: The Professor Aronnax must be constantly reminded that other people is not as good as himself. He really doesn’t want to believe that Nemo is doing something sinister, and Ned Land must remind him that the war ship that is shooting the Nautilus is doing it on purpose.
Tyentyetnikov starts as this in Dead Souls, tries to improve the lot of his serfs, with at best mixed results, and becomes apathetic in the end.
Live-Action TV
Hiro of Heroes is a careful treatment and examination of this trope.
Dr. Molly Clock in Scrubs. Partially subverted, however, in that her incorrigible optimism is undaunted in the face of the naked cynicism of Dr. Cox and Dr. Kelso, and even allows her to triumph against them.
J.D. himself might fit too, at least at the beginning.
And then there's the one-episode character from season one, who is eternally optimistic about the chances of a little boy in his care, until finally he suffers a Heroic BSOD as he realizes nothing he's tried is working and the kid is going to die.
Sam Seaborn in The West Wing. Often, he creates idealistic scenarios and goals that sound wonderful, but when he presents them to Leo or the President, they are shot down because of being impractical, a waste of time, or just plain dangerous. He also is very trusting and naive, which gets him into trouble on a frequent basis. Often, as in the case of a public education plan he developed that would have been revolutionary, he completely forgets to factor in a budget, accidentally assuming that there are no limitations. Ironically, this makes utter sense, as this seems to be the most glaring problem with entire American Dream.
New correspondent Kristin Schaal is currently playing this (along with The Woobie) on The Daily Show - it remains to be seen how long it will last, as she is cruelly disillusioned in just about every appearance.
Lieutenant George in Blackadder Goes Forth, despite having spent three years in the trenches of World War I, is still mindlessly optimistic about giving the Germans a good bashing, and readily believes all war propaganda to be true. The grim reality of his situation (in particular, the event of 'going over the top' he's been looking forward to for all the series) dawns on him when he realises that he's the only one of his class group left, all the rest having been killed. He goes over the top shortly afterwards in a Bolivian Army Ending.
His response to realizing all his friends are dead is "Well, I guess I'm the only one left... oh.... I mean, if it wasn't for the excitement of going over the top tomorrow, I might be a bit down!"
Subverted when he says to Blackadder: "Captain, I'm... scared." Up until that point, I wasn't sure whether or not this was intended to be more of the show's black humor, or if it was actually supposed to be horrifying. That line cleared it right up. Then, It Got Worse.
Naive, gentle Tora Ziyal, despite growing up as a prisoner of the Breen, despite being rejected by Bajorans and Cardassians for her hybrid status, still remains trusting and hopeful that she can somehow help, with her art that resembles that of both cultures, in proving that the groups aren't so different after all. She knows her father, Dukat's past, but loves him anyway, sincerely believing he's changed, and keeps right on forgiving him. Too bad that choosing saving her friends over staying with her father gets her shot by her father's Dragon as a traitor. Dukat goes mad as a result.
David Shephard and Michelle Benjamin both fit this trope to a T in Kings although David seems to be growing out of it.
Shinji in Kamen Rider Ryuki, caught in a fight for a single wish, Shinji fights to try and stop this but learn he could not...
Annie in Community. She even thinks her nickname is "Irony-free Annie".
Music
Billy Joel's song "Pressure" is about a Wide-Eyed Idealist and how unrealistic his hopes and expectations are.
The Tau in Warhammer 40,000 started out pretty close, before the inevitable grimmification. They still qualify in that galaxy, even though in any other they'd be the bad guys the heroes have to stop at all costs.
In the backstory of the old Battletech world, the last First Lord of the Star League, Richard Cameron was orphaned as a boy, and grew up with idealistic, Arthurian vision of his supposed role as head of the multi-kingdomed, federal empire. Since politics in the Battletech universe are much more realistic than that, he was the worst possible choice for the critical throne at the worst possible time, and catastrophe followed.
Not helped by the fact that an Evil Chancellor, who would later go on to kill Richard and bring the Star League to ruin, was warping his mind and constantly clouding his judgment towards said idealism.
Videogames
Tahlkora from Guild Wars: Nightfall. "I signed on for the heroic songs and the praise. I did not sign on for the blood-sucking bugs."
Will / Ed from Advance Wars: Days of Ruin / Dark Conflict. His idealism arguably pushes him dangerously close to being an Idiot Hero, as he is often wildly optimistic and consequently sometimes fails to look at situations properly. However, his will and sheer determination in even the worst of situations often leads to at least one crowning moment of heartwarming. Case in point - mission 16, which starts off with desperate music playing pushing ever closer to the Despair Event Horizon, when suddenly Will/Ed decides he's going to fight, and the music changes from desperate to sheer awesome.
Flonne in Disgaea falls under this trope. She never ceases to be an overoptimistic idealist who believes that demons can love, and that Seraph Lamington is a good guy.
Brother-Sergeant Thaddeus in Dawn of War II, with most of his older and wiser fellow sergeants pointing out his relative naivete at several points. In the Expansion PackChaos Rising, Thaddeus will go rogue if his Corruption level is the highest in the squad — unlike all the other squadmates, who go rogue over Necessarily Evil reasons, Demonic Possession or over bitterness, Thaddeus' corruption is revealed to be over his idealism — he willingly believed the word of a daemon.
In Deus Ex Human Revolution, David Sarif is this to an extent. In a world of high tech cybernetics, ruthless conspiracy, corporate warfare, AndBad Weather— signs that would warn a Genre Savvy individual that s/he's in a Cyber Punk setting, Sarif believes that the best thing to do with augmentation technology is to remove all restrictions on it, and that doing so will help the people of the world.
Then again, judging by Archer's comments, the past he went through seemed similar to the Fate route, so there may be a pair of Jade-Colored Glasses waiting for Shirou there...
Webcomics
Seiko from Used Books is a great example. She is constantly standing up for people tho others deem as villains. She holds fast that people are basically good, even if they have done nothing but cause hardship. She also stops in the middle of a battle to bandage up an enemy someone on her own team just injured.
Lisa from Mechagical Girl Lisa ANT is one of these... only thing is, not only she still firmly believes her life is a Magical Girl anime despite all she's been through, but she doesn't even cares about her robot outfit being actually a Humongous Mecha for ants.
Franchesca "Kid" Martines from Angels2200 is a textbook example. Not surprisingly, she almost gets booted off the squad when she can't bring herself to fire on an enemy fighter knowing she'd be taking someone else's life.
Played with in Homestuck with John Egbert. He's a wildly idealistic kid playing a game that's already destroyed the Earth and rendering it more or less uninhabitable, and being constantly accosted by literal Trolls who continue to call out the fact that the kids fail to win the game and nothing they do will change that. This doesn't seem to deter John in the slightest.
In El Goonish Shive, Grace is this in all things including nudity, and so was Susan before her Mercy Killof the aberration.Literally so — her eyes change into her current half-droopy state when she looks down at his corpse, and while she still haswideeyesquiteoften, they do tend towards the "half-droopy". After the encounter of a weird kind with Jerry led to Freak Out, though, she now tends to having wide open eyes more often than not.
Web Originals
Himei of Sailor Nothing was once a Genre SavvyAscended Fangirl of Magical Girl anime... starring in a Deconstruction of Magical Girl anime. She quickly learned (by the beginning of where the story picks up) that the job is not so much fun as it looks. Aki fills the role after Himei has become thoroughly jaded.
A toned-down version of Penny in Dr. Horrible's Sing-Along Blog. "...a generally nice person whose idealistic attempts at solving the problems of their world turn out to go horribly horribly awry..." Do I detect a bit of irony?
Emma Babineaux of the Battle Royale based RP Survival of the Fittest arguably fits this. After winning a fight against J.R. Rizzolo, instead of shooting him, she tries to convince him to stop killing and escape the island with her - this being after he attempted to murder her twice.
And then she gets killed for her troubles. Poor, foolish Emma.
Chris Davidson from v4 may indeed be this as well.
One could easily make a case for Carol Burke as well, who seems to genuinely believe they are going to be rescued and the terrorists wouldn't get away with it a fourth time. To her, very few at her school would actually play, especially her friends. Heck, she trusts ReikoIshida and like Emma, gets killed for her troubles.
Orn "Dutchy" Ayers could also be interpreted as this. However, it's also a major reason why he's considered The Woobie; he's smart enough to know that although things should be good and he wants to do the right thing, things... aren't working out. As a result, he doesn't take things very well, and spends a good portion of his time on the island in a Heroic BSOD, wishing he could save all his friends.
Western Animation
Silverbolt of Beast Wars started out as a starry-eyed idealist. He was so thoroughly chivalrous that he refused to hit or fire upon a female (Blackarachnia) even if his own life, or the lives of his comrades, depended on it. His naivete took its toll in the three-part second season finale where he refused direct orders from Optimus to capture Blackarachnia, instead going after her to help her dig up the Ark. This enabled Megatron to make it to the Ark easier and gain the access codes from Blackarachnia after threatening Silverbolt's life. Then Megatron went into the Ark and fired a fatal blast into the still dormant Optimus Prime's head, triggering a cataclysmic time storm that nearly destroyed all the Maximals and wiped out time and space. All thanks to Silverbolt's refusal to capture Blackarachnia. Later on, of course, everything gets cleaned up but Silverbolt's actions nearly led to the destruction of time and space due to his wide-optical idealism. In Beast Machines, this trope becomes subverted as Silverbolt is transformed into the villainous Jetstorm. Blackarachnia does bring him back but once Silverbolt returns, he no longer has the rosy outlook on life that he used to, becoming a bitter Anti-Hero for the remainder of the series.
It should be noted that despite leading Megatron to the Ark the first time, his continued pursuit of Blackaracnia kept her on the Maximal side all through season 3 despite some close calls regarding her Chaotic Neutral yearnings. In fact, it's only because of his devotion that ultimately she becomes a real Maximal. This ironically is the only thing that saves the future yet again when she's the last maximal to survive a mental takeover of Optimus Primal, and thus she's able to save the ark from self destruction.
Wally from the Where's Wally cartoon series fits this trope to a T but manages to avoid the horrible death part. He's too cheery for his own good and his dog Woof has more common sense than he does yet he always escapes unscathed from his dangerous journeys.
The Fantastic Racism of Manhattan is particularly painful for Angela of Gargoyles, who was raised on Avalon where humans and gargoyles live in harmony. She also hopes more than is wise or reasonable that her mother Demona can change or be redeemed.
Subverted with Yoink from the "Yoink Of The Yukon" short on What A Cartoon Show. Oddly enough, he survives and his cynical partner gets to be The Chew Toy.
Felicity in Felidae who seems to believe good in everyone despite being blind. Unfortunately...
Zeta from The Zeta Project pretty much is this trope, naive and kind, always taking people at their word, a terrible of judge of character who thinks the best of everyone and generally easily manipulated. It's due to being so young and having no knowledge of the world beforehand, and to be fair, his friends do try to help him get better about this.
Aang started off this way. But being shouldered with the weight of the Avatar Spirit, his entire people dying, Appa's kidnapping and the horrors of war quickly got rid of it.
In Transformers Prime, Optimus when he was Orion Pax as Megatron's protege in the Cybertron civil rights movement. He ended up endearing himself to the general public compared to his mentor's more ruthless methods.
