I'm watching The Dark Night with a group of friends, under a flickering light with beer in hand. Now, I'm not one for action movies - I didn't pick this one, but I need to make it more interesting for myself. So, let's talk about justice:
This movie is obviously set in Gotham City, a city rife with corruption, poverty and psychopaths. It has its own special breed of disturbed psychopaths; Poison Ivy, Bane, Two-Face, Catwoman, The Riddler, The Joker, The Penguin and Batman - a billionaire that dresses himself up as a bat and makes a valiant attempt to uphold justice and order. Batman treads a fine line between being a defender of justice and being a selfish vigilante that is trying to avenge his parents' death.
Then there's John Rawls - a 20th C political philosopher. He believed that a "just man" is committed to the view that moral obligations or duties exist equally for everyone (deontological morality). He believed that justice = fairness. Citizens were all equal and could step behind a "veil of ignorance" when determining principals of justice. When one steps behind this veil of ignorance, they are ignorant from their particular circumstances (blind, poor, rich, etc).
Let's relate this to Batman - imagine if Batman were to stumble upon on a situation where both an innocent person and The Joker were in mortal danger. He would be morally obligated (under the veil of ignorance) to treat them the same way. He can't fear The Joker because of the past and can't favour the innocent civilian - nor can he allow his Bruce Wayne bias to influence his actions. Stepping into the Batsuit effectively means stepping behind the veil. If Two-Face becomes president, and promises tax-breaks for the rich, Wayne would be swayed to support him. This rules Batman out of the vigilante category because when he puts on the suit, he puts his personal situation aside and acts in the interests of all rather than just taking the law into his own hands.
In a city as messed up as Gotham, one has to step outside the system, behind the veil in order to single handedly reconstitute it.