Did Bruce break his rule against killing his enemies in the first film?
Ra’s was on the train. Bruce sent Gordon ahead with the Batmobile to destroy part of the track. Meanwhile, Bruce engaged Ra’s in combat, which kept Ra’s from becoming aware of the gap or extricating himself from the situation.
How is that not killing?
This is what frustrates me about the part where he goes out of his way to rescue the Joker from falling at the end of TDK. I mean, he didn't do that for Ra's in BB or Harvey at the end of TDK.
He caused Dent's death directly. Yes, it was to save Gordon's son, but it was still killing, just not murder. The situation with the Joker would have been self-defense as the Joker had Batman pinned, and given his nature, might very well have killed him.
one of the things I liked about the Burton movies was that Batman was pragmatic about killing. He didn't go out of his way to kill criminals or kill them in cold blood, but he could kill when he had to.
If Nolan were really interested in "comic book realism," he'd have Batman kill occasionally, as a vigilante in his situation would probably have to do.