I too was troubled by the Joker supposedly being an agent of choas, a 'man without a plan' pulling off such intricately, impossibly detailed convoluted plans. But then I caught the movie again and I think a different take on the Joker makes better sense.

Forget about the Joker's speech to Dent. It's his final speech that reveals his true nature. The Joker is like the Devil in the Book of Job. You recall the Devil tried to break Job by tormenting him with an array of horrors. Horrors so unlikely to all happen at once that they are almost totally implausible. I think this is what the Joker is about in The Dark Knight. He pushes and tests Batman, Dent and the people of Gotham by constantly upping the ante.

When I saw the movie I was struck with how realistic it seemed. Many seens took place during the day where Batman and his gizmos look kind of silly. Gotham isn't the semi-fantastic city from the first movie or the movies in the 1990's but a pretty real looking city. The reaction to the Joker isn't all that unrealistic as you make it out. In the real world who would have expected the Joker to not only plant a bomb inside one of his cronies but also to be able to time the arrest of himself and his crony just right so that the bomb would spring him from jail? Like the Devil, the Joker's torments are realistic in the sense that we can imagine a terrorist or criminal doing any one or a few of them but there is something borderline supernatural in his ability to gather all the torments together and keep inflicting them on the victim. There's a moment when you imagine the people of Gotham saying 'no way' as they hear not only has the Joker escaped but planted a bomb in a hospital...wait blew up a hospital but now will blow up two giant ferries filled with people! How did Job feel when he suddenly woke up with oozing sores AFTER his wife died, his kids died, his livestock died, his house burned etc.

Unlike Job, the Joker is pushing multiple people. Batman mostly passes, resisting the temptation to violate his rule against killing the criminals he fights. Dent fails, allowing himself to be sold on the idea that his committment to justice was just an illusion and the world is nothing more than meaningless chance. The people of Gotham pass after both its criminals and citizens decide they will not murder others to save their own lives.