Moments where a character warns an individual that if they kill the murderer, they will be just like him/her in Literature.
- Nightfall (Series): Myra has a chance to kill Prince Vladimir, but in a very dishonorable way that would destroy her humanity. Different from most examples because the war is not over and killing the Prince would make a difference.
- Animorphs:
- When the war ends, Jake refuses to kill Visser One. Tobias, enraged, demands to know why, claiming that Visser One was the one responsible for the entire war. Jake replies quietly that they "don't kill prisoners."
- The Visser immediately mocks his hypocrisy; Jake has just killed seventeen thousand unarmed, helpless Yeerks. Not to mention he and the others had blown up the shopping mall to take out the Yeerk pool beneath it, which killed thousands of unhosted Yeerks and hundreds of innocent people.
- Rachel is about to kill Tobias' captor Taylor, but Tobias urges her: "Be Rachel. Not her."
- In Harry Potter and the Prisoner of Azkaban, Harry stops Sirius Black and Remus Lupin from killing Peter Pettigrew, who had betrayed Harry's parents' whereabouts to Voldemort, because he was sure his father wouldn't have wanted his old friends to become murderers, even in revenge for his own death. Notably, however, he didn't regard this as any kind of mercy for Pettigrew's sake, and was happy for him to go to Azkaban prison. Sadly, unforeseen circumstances interfere and Pettigrew escapes with ultimately disastrous long-term consequences, though the 'mercy' itself has slightly more positive results.
- Babylon 5:
- In the novel "Final Reckoning: The Fate of Bester" this is what stops Michael Garibaldi from killing the telepathic war criminal Alfred Bester after the telepathic blocks keeping him from taking revenge on Bester are removed and Garibaldi catches up with him outside Paris. This is after Bester mind raped Garibaldi, turned him against his friends and colleagues, and oversaw experimentation on sentient beings that would have made men like Josef Mengele sick, so not many people would have been in mourning if Garibaldi had killed Bester. However, Garibaldi decides there are other victims who have equally strong claims, he wants to be the kind of man his daughter would be proud to call her father, and to not sink to Bester's level.
- A variation is used in book two of The Bartimaeus Trilogy: the neutral (or so he claims) djinni Bartimaeus persuades Kitty to save Nathaniel by hinting that, 'If you let him die, you'll be just like me.'
- In Chasing Shadows, Holly's visions show her that Savitri killing Wiry would make her just as bad, at least to Kortha, and she pleads with her not to do it.
- Used in Komarr by Lois McMaster Bujold. Komarran terrorists are about to activate their new weapon, which they think will lead to a bloodless coup, but which will actually blow up the space station it's positioned on, in revenge for the Barrayan massacre of Komarran hostages a generation ago. When the army closes in, they threaten to murder their hostages, Ekaterin Vorsoisson and Aunt Vorthys, if Imperial Auditor Miles Vorkosigan doesn't order the army to back off. Miles tells them, "Please observe that you have now gone as far as you can without turning yourselves into a perfect replica of the enemy you set out to oppose." The terrorists surrender, but partially because Ekaterin had already destroyed their device.
- In The Dresden Files universe, the highly addictive nature of black magic means the White Council enforces this for any type of magical killing of a human. So, someone who uses black magic to kill a human, even if that human was a black-magic murderer themselves, will almost always jump off the slippery slope and become a serial murderer themselves.
- It's worth noting that this applies specifically to using magic to kill. The Council couldn't care less about a wizard using mundane means like, say, a gun to do the same and is itself altogether too fond of enforcing its own death penalties for breaking the Laws of Magic (typically by beheading) even at the first offense for Harry's comfort. This is because any magic which breaks said Laws results in The Corruption, which is permanent and cannot be removed. We get to see it first hand several times, and it is never pretty. The White Council also possesses a magical artifact known as the Black Staff, which prevents said corruption. They use it liberally.
- In Fool Moon there's an aversion: When Tera West hears this line she replies, "No I won't. I'll be alive, and he'll be dead." It's likely intended as one hint among several that, unlike all the other werewolves in the book, she's actually a wolf who can take human form.
- It also pops up in short story The Warrior, where Michael has a Sword over Head moment with the man who kidnapped and nearly blew up one of his daughters. Harry talks Michael down, saying he's already beaten and harmless, that's not who he is and if the man really has to die, to let Harry do it.
- Discworld:
- Jingo implies that Sam Vimes believes something like this. He's all right with killing someone by accident, but a pre-meditated killing leaves him deeply troubled. In the next City Watch book, Night Watch, the Gargoyles parallel is even more explicit, as he's now shown to be perfectly willing to kill other people intentionally when he's in the middle of a pitched battle.
- In The Fifth Elephant, he has no choice but to kill Wolfgang but refuses to deliver any of the Bond One Liners that came into his head because he feared becoming what Wolfgang was.
- Another Terry Pratchett book, Nation, has this discussed as a theme, though the focus is more on the thinking like the villain, than the actual act of killing. First Mate Cox is cruel and evil, enjoying killing simply for the joy of it. When he mutinied against The Good Captain, said captain nearly fell for this trope. Later, Mau is afraid of thinking like him, but decides that any hunter must think like their prey, yet does not turn into it.
- The Bandakarians in the Sword of Truth book Naked Empire believe something akin to this in relation to all killing. Including that in battle.
- Subverted in Shadow of the Giant, when Bean grabs Volescu, a man who tried to redesign the human race by replacing them with people like Bean: super-smart but doomed to die by age twenty or so, and also is directly responsible for Bean being like that, by the throat and threatens to kill him:Petra: Please don't kill him, Bean. Please.
Bean: Remind me why.
Petra: Because we're good people.
Volescu: [laughs] You live by murder. How many people have you both killed? And if we add in all the Buggers you slaughtered out in space...
Petra: Ok, go ahead and kill him.- They end up not killing him in the end, if for no other reason than he has information they need.
- In book ten of A Series of Unfortunate Events, with Sunny captured by Olaf and one of his top goons heading towards them, the kids decide to set a trap to gain a hostage of their own to possibly trade for their sister. But before they do it, they have an epiphany: if they capture this woman, it will make them evil like Olaf, so they surrender to her and she takes them to Olaf. And these kids are supposed to be the smart ones in a world of useless adults.
- Star Wars Legends:
- Unintentionally invoked by the Dark Jedi Yun after he's defeated by Kyle Katarn in the novelization of the PC game Jedi Knight. After Kyle disables Yun's sword arm, the younger man spits "So, kill me, Rebel, just as I would kill you!" Kyle is about to, when he realizes that he doesn't want to do what Yun would. He doesn't want to be the kind of man who would kill without reason, and Yun is no longer a threat. This act of mercy also starts Yun on the path to his Heel–Face Turn (and, unfortunately, Redemption Equals Death).
- Obi-Wan's dilemma towards the end of Star Wars: Kenobi. Let Orrin Gault go free and he'll tell the entire galaxy that there's a Jedi hiding on Tatooine, but killing him just to keep him silent isn't in his nature either—it's "something you would do." He eventually takes a third option.
- In the Legacy of the Force Luke wants to be the one to confront his nephew Darth Caedus (fka Jacen Solo) for murdering his wife Mara Jade. But he realizes that no matter what if he kills Caedus he would become even more of a Sith Lord than Caedus already was. This is a major factor in his deciding to leave confronting Caedus to the Sith Lord's sister Jaina.
- In The Pendragon Adventure, it's brought up several times by characters that Bobby, as leader, shouldn't become a killer. You'd think it was the usual argument about morals, and being just like Saint Dane, and it partially is, but in the second to last book, when Bobby, blinded with rage, pushes Naymeer out of the helicopter, it's revealed that him taking a life was the final step needed for Saint Dane to take over all of Halla, which is everything that does and ever will exist.
- Star Trek:
- In the Star Trek: The Next Generation novel "Reunion" Commander Idun Asmund is talked out of killing the insane Doctor Carter Greyhorse - who had been trying to kill Picard and the visiting USS Stargazer survivors - by appealing to her intact honor and that to kill Greyhorse would be to sink to his level. When Greyhorse tells Idun that her sister Gerda would've killed him, Idun tells him that Gerda had too much honor to kill a madman.
- Played with in Star Trek: The Genesis Wave. The Bolian colonists on Myrmidon have seen their planet terraformed into an uninhabitable jungle by the Lomarians. When they fight the Lomarians by setting the jungle alight, becoming frenzied and desperate, Mr. Mot sadly reflects that they've sunk to the level of the enemy; single-mindedly destroying an entire environment and those who call it home. However, while he acknowledges that his people are indeed "just like" the Lomarians, and is saddened by it, he doesn't actually condemn them or say they were wrong; at least in this case, becoming "just like him" is seen as a sad necessity.
- In The Dragon In The Sword, by Michael Moorcock, the heroes have the villainous Sharadim at their mercy, and use this as their reasoning to merely kidnap her as a shield for their escape out of her domain, rather than killing her outright. It's presented in a more justified light, though: she had just had callously murdered some of their allies, and to now slay her the same way would have made them no better, and lost all their justification in their struggle against her. In effect, it's not killing that's presented as bad - it's murdering a helpless victim (even if villain) in cold blood and with no honour or justification.
- The Legend of Drizzt: Drizzt Do'Urden has been in a position of wondering whether to spare his Arch-Enemy Artemis Entreri, considering leaving him alive also as potentially unethical because he's just going to kill more innocents if he lives. Not that it matters much what he decides, as Entreri has Joker Immunity. Drizzt also used to be determined never to kill his fellow drow, because that's what they always did to each other and that was what he didn't want to become like. Once they catch up to him in his new life and start attacking, though, he quickly stops angsting over that because it would be stupid. Basically, he realises it's not this trope when it's self-defence.
- In Sarah A. Hoyt's Darkship Thieves, Thena wants to kill her father, both for justice and because he wants to transplant his brain to her body. She fails. Kit points out that it proves being his clone didn't make her like him.
- In Veniss Underground, Nicola invokes this when pleading for Salvador not to kill her:Nicola: Do you want to be as cruel as those humans in your holograph show? To be no better than the worst of what we are?
- In The Golgotha Series, a recurring theme of The Shotgun Arcana is heroes having villains at their mercy but choosing not to kill them because, as heroes, they have to hold themselves to a higher moral standard.
- In Chance And Choices Adventures, the bandit Gus has attacked the heroes countless times, burned down their farm, was finally captured and is being transported to Little Rock for trial when he attacks again and tries to strangle Ann with a chain. Noah stops the attack and tries to strangle Gus back, only to be stopped by Sheriff Smitty who insists that everyone deserves a trial and even completely evil people can't just be executed out of rage.
- Warrior Cats:
- In Forest of Secrets, when the other Clans demand to know why ThunderClan is sheltering the evil Brokenstar, Bluestar explains that killing a blind, defeated cat (or leaving him to die in the forest) would make them just as bad as Brokenstar himself was.
- In Veil of Shadows, the rebels discuss whether to kill the impostor-Bramblestar; Bristlefrost points out that if they do that, they'll be no better than he is.
- Ferals Series: In The Swarm Descends, Caw decides not to kill the Mother of Flies, realizing that in doing so, he would be orphaning Selina, similar to how he himself was orphaned by the Spinning Man.
