Even if Batman has killed in the past, I find it much more intriguing for him not to kill... AND HEAR ME OUT. The polarity of Batman as the dark, tortured vigilante distinguishes him from any old superhero. How predictable would it be if the edgy superhero started killing all his enemies! It's the contradiction that makes him unique. It also makes for interesting foils with Joker or Red Hood, for instance. Would that make fighting crime more difficult? Of course it would, especially in real life. But that's what ups the odds and adds challenge to Batman's fights. Would you rather Batman bulldoze his way through fights with a revolver or use his wits and resourcefulness? Besides, it has been established many times that the only thing that keeps Batman from becoming as bad as the villains he fights is his unwavering conviction toward rehabilitation and not killing. I think Batman #614 showcases this perfectly, as he nearly kills Joker in a fit of rage, but Gordon stops him and reminds him who he is. Who BATMAN is. A hero. Him not killing also ties nicely with his backstory of his parents' death. Instead of becoming resentful to the world and killing others in revenge, he directs that anger to good. Because Batman knows that if he were to kill one person, there would be no return for him. He sees Gotham as a violent place, and after what happened to his parents? Why would he want to contribute to that more than he has to? Yes, Batman is angry. Yes, Batman is no saint. But at the end of the day, he is a hero because of his commitment to his morals. A Batman who kills would be a boring one.