Why did Batman save the Joker in “The Dark Knight” and not save Ras al Ghul in “Batman Begins?
Ra’s al Ghul was responsible for being on the monorail; Batman himself threw the Joker off of the building. In the first case, Ra’s put himself in the situation which resulted in his death; whereas in the second case, had Batman not saved the Joker, he would be solely responsible for murdering him. Doing so would have been a violation of his one rule, “I will not be an executioner.” It is also possible that Batman was trying to prove to the Joker that he was incorruptible. The Joker even makes it a point after Batman saves him to say “You are truly incorruptible.” Refer to the 3rd interpretation in this FAQ entry for a detailed explanation.
