Moral Event Horizon:
- The Joker's always been a psychopath, but he definitely crossed it when he killed Rachel Dawes, which then led Harvey Dent to insanity.
- The organized crime community as a whole arguably crossed this by hiring the Joker in the first place (and the Chechen crosses it by making the decision to hire him), as was implied by one of Bruce Wayne's lines following the deaths of Loeb and Surrillo, a line used in one of the earlier trailers...
Bruce Wayne: Targeting me won't get them their money back. I knew the mob wouldn't go down without a fight, but this is different. They've crossed a line.
- In fact, the only mobsters who don't cross the MEH are Sal Maroni, who only let the Chechen hire the Joker because of Lau's capture and only refuses to rat the Joker out to Batman because he's truly scared of the Joker ("Have you met this guy?"); Gambol, who knew from the start that the Joker was bad news not just for Gotham but for its organized crime community as well and actually stood up to the freak; and the Gotham National Bank manager, who bravely stands up to the Joker during the bank robbery and ices Chuckles (and tags Grumpy in the shoulder), to say nothing of what he thinks about the endless backstabbing he witnesses throughout.
- Harvey Dent threatening to kill Gordon's family in front of him at the end of the film. Despite attempted reasoning from Batman, he refuses redemption full stop, leaving the former no choice other than shoving him out the behind window to his death.