Even though Superman has the power to annihilate his foes, he purposely avoids landing killing blows in comics. However, in Man of Steel, Superman does the unthinkable and snaps General Zod's neck. In this moment, Superman became a killer, but he's not the only hero to succumb to his more lethal urges.
In Batman Begins, Bruce leaves his mentor Ra's al Ghul to die on two separate occasions. Black Panther stabs Killmonger and makes minimal effort to save his life despite abundant resources in his titular film, while Ant-Man brutally shrink-crushes Yellowjacket in his. Although being a superhero is a dangerous job, it seems that being a supervillain is actually the far more perilous profession, on the big screen at least.
Valuing human life is often a quality that separates superheroes from the villains they face. While bad guys murder and destroy, superheroes protect life even when it is difficult. Why is it then, that so many villains seem to die or even get killed by the superheroes they fight? Not only does having a superhero killing a villain undermine the moral qualities of superheroes, it also creates odd inconsistencies in the universes of these stories.
In the comics that these superhero movies are based on, being a superhero is about much more than simply having supernatural powers.
Many genres of media like horror and fantasy have characters who can do the impossible. What truly separates superhero stories from other stories is not super powers but their moral codes. A superhero is someone who embodies aspects of humanity to an incredible level. Some heroes embody one particular aspect, like Green Lantern's willpower, while others, like Captain America, are paragons that demonstrate the full range of positive human characteristics.
To be super-human is just that, to be more human than a regular person. And one of the most important aspects of humanity is to protect and save other human lives. So a superhero should embody the valuing of human life to a superlative degree. Death is the enemy, something that villains try to do and heroes prevent. In comics, plenty of heroes have a credos about not killing, but such values seem to get tossed aside once a superhero makes it to the big screen.
Superhero films typically do a decent job of showing superheroes saving regular folks, but when it comes to fighting bad guys, things often get mortally violent. In a good portion of superhero films, the heroes are usually directly or indirectly responsible for the death of the main villains.
Whether it’s a direct killing of a villain like the infamous neck snap in Man of Steel or Tony Stark indirectly killing Iron Monger in his first film, superheroes have accumulated a considerable body count, while many of those slain villains usually escape to fight another day in comics. Although portraying death on screen certainly elevates the stakes cinematically, it creates several two problems for the genre.
First, having superheroes contribute directly or indirectly to the deaths of villains undermines the humanitarian qualities of superheroes, leaving them merely superpowered action stars. Although superhero films certainly address some dark themes, they aren't supposed to become so dark themselves that viewers can't see the light.
In director Zack Synder's DC films especially, fan-favorite heroes are seen taking part in brutal, almost merciless violence. Even when it's justifiable, like in Wonder Woman, it can still leave a bad taste in your mouth. but the MCU isn't innocent in this regard either. The Thor series has had its fair share of slayings, even in the cinematic adventures of Iron Man, Thor and Captain America. Although a part of us wants to see villains get their comeuppance, superheroes should encourage us to be better, and valuing the life of someone who doesn’t deserve it shows the true depth of goodness in a character, and that’s what makes superheroes so inspirational.
With so many villains dying by the end of the movies they appear, superhero movies also have some weird, narratively incongruent moments that could be otherwise avoided. In director Christopher Nolan's films, which explicitly state Batman's no-kill rule by name, there are moments where Batman seems to be fine with firing clearly lethal missiles at his enemies or leaving a nemesis to die without saving him.
Another example of the weirdness created from situations like these is when the MCU introduced the Raft in Captain America: Civil War, which is an ocean based prison for supervillains in the comics. In the film, however, there weren’t really any villains to put in it, so the supervillain prison just ended up housing superheroes.
Now while it is certainly true that it’s not feasible to have the actors who play villains on retainer, simply having a cell with the name of a captured villain on it would be a nice Easter egg, like in All Hail the King, the short film featuring the fake mandarin from Iron Man 3. But moments like that are only really possible if superheroes stop killing bad guys.
While it would be nice to see villains go to prison instead of a graveyard for their crimes, less lethal heroes could bring some of the hope and wonder that they've inspired in generations of comic readers to the big screen.