One of the great things about Christopher Nolan's Batman franchise is that he tries to take these amazingly cartoonish "Pow" "Bam" "Boom" comics, with some of the most cartoonish characters (Joker, Two Face, Scarecrow, Cat Woman, Poison Ivy, the Riddler, and the Penguin), and make these cartoonish characters real.
In the Dark Knight, trying to make the Joker a real, less cartoony villain is certainly a challenge and part of where the real magic of this film comes in. Heath Ledger's casting originally made people scratch there heads (for kicks, read the comments when I announced the original Ledger casting decision).
Yet, the way that Nolan has handled Batman is far different than say Spider-Man, X-Men or this years popular Iron Man. In Spider-Man the rational for super heroes and villains related back to science and personal vendetas after freak accidents. X-Men is a fun concept that in many ways deals with genetic mutations, again with science, but these super heroes and villains are trying to discover there place in modern society. Iron Man, in many ways has some of the same threads of early comics that came out during WWII, in that it combines super-hero powers with national pride and fighting military villains.
The Batman story, especially told in a modern world that is supposed to "seem real" means that these super-villains have psychological problems. In a court of law it would be incredibly hard to pin point Joker's true motive in a way that could be proven with court documents. Instead they would be forced to use circumstantial evidence to try to create a case for the Joker's insanity and psychological motives that lead him to commit crimes. In reality, the story is similar for the majority of Batman's villains, although some cross over into the types of villains previously mentioned (Penguin is a little bit of a freak like X-Men characters, and Two-Face is psychologically schizophrenic and unlogical, but he does have a little bit of a personal vendetta to fight for...but he takes it to a psychological extreme).
In the Real World: Bruce Ivins, Potential Anthrax Killer
When I was listening to stories about Bruce Ivins, and the Justice Departments case against Ivins as the believed Anthrax killer of October 2001, I couldn't help but draw connections to the Joker. Maybe the initial connection came with little connections, like Heath Ledger dressed as a nurse in a hospital, or Ledger's Joker placing DNA samples on a playing card to announce his next move. But the biggest connect to me comes in the challenge that the court system has in identifying Ivins' motive.
There is a significant amount of circumstantial evidence of Ivins' craziness, including his obsession with a sorority, Kappa Kappa Gamma, and his poem version of I'm a Little Teapot.
This mentally unstable poetry to the toon of I'm a Little Teapot with a Dr. Jekyll and Mr. Hyde nature sounds like it could totally come out of a Super Villain movie:
"I'm a little dream-self, short and stout.I'm the other half of Bruce-when he lets me out.When I get all steamed up, I don't pout.I push Bruce aside, them I'm free to run about!"
And I find myself drawing this correlation, and wonder if anyone else does? But it seems like some of the most dangerous, and scary issues of local and national crisis seem to be when one person, with psychological derangement uses his knowledge for evil.