Maybe I wasn't clear. I get that superheros don't kill and I get why. That wasn't what I wanted to focus on. My main point was why do superheros sometimes go out of their way to save the villain? If Joker is running from Batman and trips and falls off a building, Batman doesn't have to catch him. No court, moral or otherwise, would say that Batman killed Joker in that case. Society would be spared from Joker forever and Batman's conscience would be clear. Win win.

Yet in The Dark Knight, I'm pretty sure Batman catches Joker from falling at some point. This just does not make sense to me. Why waste your time saving someone who does not deserve it?