How we cite our quotes: All quotations are from The Dark Knight.
Quote #4
DENT: The night is darkest just before the dawn. And I promise you, the dawn is coming.
Here's Dent spelling out his duty in the clearest possible terms. He wants to bring hope to Gotham, to prove that criminals don't run the streets and to give decent citizens a chance to live their lives in peace. As we've seen, that goes seriously pear-shaped on him by the end.
Quote #5
MARONI: You got rules. The Joker, he's got no rules. No one's gonna cross him to you. You want this guy, you got one way. But you already know what that is. Just take off that mask and let him come find you. Or you gonna let a couple more people get killed while you make up your mind?
As Maroni snidely points out, every action has consequences. If Batman wants to save lives, it might mean taking off the mask, a duty that we're guessing ole Bats is going to ignore. Sadly, Maroni's right about one thing: doing so means that other people are going to pay the price.
Quote #6
THE JOKER: I wanted to see what you'd do. And you didn't disappoint. You let five people die. Then, you let Dent take your place. Even to a guy like me, that's cold.
The Joker gets at Batman here by suggesting that he's fallen down on his duty, and taken the selfish route by staying hidden rather than revealing himself to the world. It's a false analogy. Batman's unmasking would leave the city helpless before the Joker, but it makes the same point we've heard elsewhere. Batman's duty will cost lives, and not just his own.