One of my favorite aspects of "Dark Knight"

First off, Dark Knight is a masterpiece of film making, not just of the superhero genre.

One of my favorite scenes of the movie was were Christopher Nolan set up a kind of "Prisoner's Dilema" scenario.

The "Prisoner's Dilema" is a Game Theory scenario where two suspects are brought in for questioning. A confession by at least one of them is needed to bring a conviction otherwise they are both released. Each prisoner is offered a lesser sentence is they testify against the the other. If they both confess their sentence isn't reduced as much but will still be less than if they stay quiet and thier accomplice doesn't. Neither suspect knows the other suspects decision. In theory the police will get both suspects to confess because the risk associated with not confessing is to high.

In Dark Knight this scenario is played out in the scene with the ferry full of law abiding citizens and the ferry of convicts. The purely rational outcome would have been both detonators being pressed almost immediately. The actual outcome laid out in the movie is actually the more realistic in my opinion. Our ability to trust others to be good actors, even when incentives exist for them to not be, is the key to civilization. Our trust isn't always rational, but it is what allows us to relax enough to progress. The ferry scene is a good metaphor for a world where people with nuclear weapons don't actually use them against others.

Of course in my mind, the Joker rigged the trigger to detonate the boat it was on and not the other ferry.