Steve Rogers: I don't wanna kill anyone. I don't like bullies. I don't care where they're from.
This trope is largely averted. While the various heroes portrayed to date have different rules of engagement, only a few of them so far follow the classic superhero idea of never ever using deadly force. The rest, effectively being superpowered soldiers, will often kill to protect their own lives and those of the innocent. Generally speaking, heroes in the movies are willing to kill, heroes on TV don't (even in the Netflix series). Most of the superhero stories in the films are treated as military engagements and the heroes follow The Laws and Customs of War which do condone violence against enemy combatants.
- The Hulk, despite his uncontrollable rage, can restrain himself from using lethal force against a clearly evil opponent - in The Incredible Hulk, he spares Blonsky at Betty's plea. In Avengers: Age of Ultron, Banner is clearly distraught with having to hurt people as the Hulk; when Thor lets it slip that Banner killed some HYDRA agents in the opening battle, he quickly backpedals. That said, Thor: Ragnarok outright states that the Hulk killed his fair share of challengers during his time as a gladiator on Sakaar.
- After ten movies and three seasons of TV, Daredevil is the first hero to make an explicit point about it, though he finds himself sorely tempted after a while and even makes attempts when his Berserk Button is pressed. Season Two makes a point to analyze this rule by contrasting him with two remorseless killers, the Punisher and Elektra.
- Jessica Jones tries to avoid killing Kilgrave, partially for pragmatic reasons as she needs proof of Kilgrave's mind control to use in court to clear his victims. Being traumatized by killing under Kilgrave's control undoubtedly also makes her want to avoid doing it again. However, it becomes clear that trying to find a non-lethal solution just allows Kilgrave to ruin more lives. Jessica finally stops him by snapping his neck, which is treated as regrettable but necessary.
- Luke Cage flat out doesn't kill anyone. Even when he has been tempted, he doesn't go through with it. For example, when he attempts to kill the bus driver who he believed to have been the one who killed his wife Reva, he is stopped from killing him by Jessica. Also, he does choke Scarfe when he confesses to killing Chico, but doesn't go through with killing him. Otherwise, he generally just knocks out criminals without killing them. On top of that, he Doesn't Like Guns and bends them into pretzels whenever he gets the chance.
- Stephen Strange takes his Hippocratic Oath very seriously. In his debut film, he is unnerved when he is forced to kill one of Kaecilius' zealots, and even more appalled that Kamar-Taj outright advocates the use of force to combat their enemies, both in self-defense and proactively. By the end of the movie, Strange is able to defeat both Kaecilius and Dormammu without resorting to lethal methods — though Kaecilius' defeat involves a Fate Worse than Death.
- During his training in K'un-Lun, Danny Rand was taught that the Iron Fist was to kill the Hand without hesitation or mercy. However, throughout Iron Fist, Danny struggles with whether or not he can kill someone. Ultimately, Danny decides that he can kill someone, but is making the conscious choice to not end their life.
- The Avengers mostly avert this. They will kill in combat conditions but it's also only in a last resort against opponents who are themselves predisposed to violence and use lethal force against the Avengers and bystanders. As Natasha tells Proxima Midnight at the start of Infinity War:Black Widow: "We don't want to kill you, but we will."
- Captain America is a soldier and, during World War II, thinks nothing about using guns and other weapons in combat, best shown in the montage where he's firing a Thompson alongside the Howling Commandoes and dropping grenades inside a HYDRA tank, and hurling Hydra stooges into rotor blades in the final chase inside Red Skull's ship. Post-that however, his main weapon is his shield which is not a directly lethal weapon, although Cap does find ways to use it for lethal ends in the right situation such as the highway fight scene in Captain America: The Winter Soldier where he deflects bullets at others which kills them.
- Hawkeye and Black Widow are spies and assassins, while War Machine and the Falcon are professional soldiers, therefore it's not surprising that they use guns and other lethal weapons all the time. In Endgame, Hawkeye goes on a mass-murdering killing spree attacking gangsters around the world who he believes didn't deserve to survive the snap instead of his family.
- Iron Man thinks nothing about using deadly force in order to defend himself or others, as shown in his first movie when he incinerates many of the Ten Rings during his escape. This is particularly demonstrated in Spider-Man: Homecoming, where Peter Parker discovers that the Spider-Suit Tony made for him has a "insta-kill" mode when its "training wheels" protocol is disabled, indicating that he expected a grownup Peter would use deadly ordinance as an Avenger. However, Tony still sticks to using lethal force only in self-defence, rather than in cold blood: when a henchman in Iron Man 3 puts his gun down and asks to walk away, Tony just lets the guy go.
- Thor is from a proud warrior race, and thus has no compunctions about killing his enemies if necessary. His own estimate of how many enemies he's killed is 3000, which given that he is about 1000 years old and is a seasoned warrior, is proportionately much smaller and lenient for a member of the Viking society's pantheon.
- Vision is polite and empathetic, "on the side of life", but he doesn't hesitate to brutally impale Corvus Glaive when Corvus is threatening to kill Captain America.
- Scarlet Witch, even after becoming an Avenger, will kill to protect her teammates. Just ask Proxima Midnight, who Wanda more or less fed to a meat grinder to keep her from killing Widow. Shes also explicitly about to kill Thanos until he pulls out a dirty trick in the climax of Endgame.
- Of course this is muted in The Avengers and Avengers: Age of Ultron, since their enemies are armies of aliens and killer robots respectively, so What Measure Is a Non-Human? applies there. Avengers: Infinity War, meanwhile, has the heroes fighting against a threat that will literally destroy half the universe, so lethal force is more than okay as a Godzilla Threshold. Avengers: Endgame doubles up, and the final battle is against an army of aliens (where the bulk of them, the Outriders, are non-sapient animals) who are actively trying to end the universe (bringing back the Godzilla Threshold).
- Avengers: Age of Ultron takes note of this: one of the first lines out of Ultron's mouth is that the Avengers are "all killers".
- The Guardians of the Galaxy are another group that averts this. They originated as criminals, mercenaries and bounty hunters and have zero qualms with killing even small-fry enemies, much less genocidal warlords like Ronan the Accuser or Omnicidal Maniacs like Ego the Living Planet, whose deaths are more or less the only way to prevent galactic destruction.
- Ant-Man plays this mostly straight, entering battle without any weapons and learning how to pull his punches just enough that he doesn't kill his enemies with his Super Strength. He also avoids using his Shrink Ray discs on living people, since shrinking is deadly and gruesome to those without the Required Secondary Powers (which are all provided to Ant-Man by his suit), only using one such disc against Yellowjacket (whose own suit protects him from any deadly effects and lets him grow back to normal size). In the end, Ant-Man can only take down Yellowjacket via lethal force, killing him by destroying his suit's regulator and blowing it up. However, he had already exhausted all his other options, and he was prepared to die in a Heroic Sacrifice since defeating Yellowjacket required a Dangerous Forbidden Technique. He also has killed enemies in the Final Battle of Endgame - particularly stepping on Cull Obsidian
- Peter Parker in Spider-Man: Homecoming of course plays this trope very straight, being that he's a Marvel character heavily associated with the trope (indeed, he's up there with Batman and Superman as one of the most famous "no-kill" heroes), even going out of his way to Save the Villain Vulture. He also flat-out refuses to use the deadly measures put in place by Iron Man in his new suit. However he is willing to make exceptions if the situation is despite enough, as seen in Avengers: Infinity War, he comes up with the plan to kill Ebony Maw by tossing him out the ship's airlock. He also explicitly kills Thanoss Outriders in Avengers: Endgame where Spider-Man finally activates his suit's Instant Kill mode against them when they dogpile him for the Iron Gauntlet.
- T'Challa, having been raised as a warrior, has no qualms about killing either, but ends up sparing the supervillains for various reasons. Zemo survived as a combination of Cruel Mercy and avoiding falling victim to revenge, while Klaue was only spared since it would've been seen by dozens of citizens and would've reflected poorly on the newly-crowned king. He also offered to heal Killmonger to avoid repeating his father's sin, but Killmonger decided to pull an I Die Free moment and finished himself off.
- Carol Danvers is in much the same boat as the other heroes with military backgrounds like Captain America, Falcon, and War Machine. Her hands are drenched with the blood of Skrulls she killed as a member of the Kree military. After leaving the Kree, she is still willing to kill if necessary, though her power level makes this less of a requirement than most other heroes.
- Agents of S.H.I.E.L.D.: Since the heroes are essentially police, they always try to avoid killing when they can, but are not hesitant about doing so when they have no other choice. Fitzsimmons invented a stun gun (initially called the "Night-Night Gun," soon upgraded to "ICER") that they use as often as possible, but a number of their enemies are immune to it for one reason or another. And of course no one cares when they slaughter HYDRA mooks by the dozen.Coulson: Mr. Yin, we don't want to hurt you.
[Scorch prepares to set him on fire]
Coulson: But we have to.
[May stabs Scorch with syringes that will make him explode]