The Dark Knight is a good movie, considerably more intelligent than one expects from the film industry these days. And Heath Ledger's performance is all they said it is. In fact, it is so good that Ledger has replaced Bruce Dern as Longhair in The Cowboys as my favorite movie villain. And that's saying something; Dern held the title for 36 years.
I don't think Steorts quite understands the Joker. This is what he says about him:
But that's not right, because the Joker doesn't do just anything. What he does is destroy. He is not chance, for chance might treat you well. He is, rather, a vandal. Why he wants to vandalize is not clear. Beyond question is that he thinks there is no such thing as right or wrong.
The Joker isn't a vandal, because a vandal is a barbarian who just wants to have a good time sacking a city. The Joker, in fact, doesn't actually do a lot of destroying. What he really wants to do is corrupt, or, more precisely, expose the corruption that is a hidden reality in all of us. We might call him a connoisseur of Original Sin.
Like all villains of his type, the Joker claims to be a "realist" but he is really a secret idealist. For the idealist, only the perfect is worthy of respect or even deserves existence. Since nothing is perfect on Earth, especially men, the idealist thinks it an abomination that the world exists at all. He can't understand how someone like Batman would spend his life defending men even in their state of corruption. He thinks it must be that Batman doesn't really understand the depth of corruption in men. So the Joker makes it his task to expose the corruption in men, and makes it his special task to corrupt even the few men who seem to be purely good. And he the Joker is pretty good at being bad.
But Batman, like Christ, has no illusions about the nature of men. The difference between the Joker and Batman is that Batman thinks men are worth saving even though they are corrupt. A better name for the film might be the Dark Christ because Batman, like Christ, sacrifices himself for men who are not as good as him.
The film does an excellent job of showing the two sides of the dual nature of man. Yes, even the best men have some store of evil in their hearts; but the converse is also true, that even evil men have some store of goodness in their hearts. The Joker sets up several "no-win" situations intended to expose the selfish nature of men, but he is (occasionally) thwarted by the surprise appearance of virtue in places one would least expect it. Good is as real as evil; in fact, it is more real.