That's the problem with adapting superhero comics to movies. American action movies are so deeply immersed in the habit of portraying protagonists using deadly force, and they insist that adapted material conform itself to existing movie conventions. Which leads not only to things like superheroes killing, but things like superhero origin stories being turned into revenge narratives rather than stories about rescuers and protectors. Even Marvel's movies have their heroes kill the bad guys routinely (Ant-Man being something of an exception, though I think there were a number of unconscious bad guys who may have implicitly been left in the building when it imploded), although at least they remember to keep the action focused on protecting civilians.