I just wish we knew WHY Dent was such a "White Knight". Jim Gordon is a much better candidate for that post, he puts up with a lot worse stuff than Dent. Why was Dent so much better loved and respected and considered "better" than Gordon?
In fact, in the original story that they based the whole "Joker tries to corrupt good guy" plot off of, he WAS trying to make Gordon crazy.
Gordon (and the police) arrest the bad guys and that's as far as their job has to go. Dent, as the DA, has to build the case against them to put them in jail. That makes his role in the process a bit more important.