1. Consequences
Nothing has effected Batman more than his family being put in danger. In fact, Batman has only twice truly considered using deadly force; both times on the Joker, and both times because his family was threatened. When Jason Todd was killed by the Joker, Batman came within inches of killing the Joker, only failing to do so because he disappeared in a fiery explosion. More recently, Batman nearly killed the Joker after he poisoned his whole family. Batman has always been a crusader for good, but his most interesting trials come when things get personal.