How we cite our quotes: All quotations are from The Dark Knight.
Quote #10
THE JOKER: You won't kill me out of some misplaced sense of self-righteousness. And I won't kill you because you're just too much fun.
This is as succinct a definition of their philosophies as we're likely to see. Notice also how, with Batman's "one rule" about not killing people proven beyond the shadow of a doubt, he chooses to mock it. Pretty sour grapes from a guy who broke Harvey Dent's psyche in half just a few hours earlier. It's also a sign amid all the darkness and despair that Batman's principles are important, and can stand up to a guy as bad as this.