One of the most important elements of most mainstream superhero comics is this: The good guys don't kill. Granted, it has not always been this way. Batman, for example, famously utilized guns in his earliest adventures, and had no compunctions about putting criminals six feet under. The no-killing thing was actually born out of the need to appease politicians who feared that comic books might turn America's youth into homosexual communists or whatever. But in the ensuing decades, creators found a way to both justify and make the most of it, using the heroes' refusal to end lives as both a potential weakness to be exploited and a subject to be debated. In other words, it has become one of the dramatic and philosophical cornerstones of superheroes as represented in that medium.