To be fair, Dick's emo over those things was basically shown as, if not idiotic, unnecessary. And I think it was shown to have less to do with morality than with the lessons Dick internalized from Bruce, which Bruce needed because he's a different person, if that makes sense. I think Bruce's personal no-kill makes sense for him as an individual who knows his own weaknesses. Dick has different weaknesses, so to him the lesson became more about Bruce than about his own thoughts about the morality of killing someone like the Joker. He let Bruce down by killing, in Bruce's eyes that makes him no better than the Joker. (Not really true, but in Dick's head imo.) As Bruce said at one point, he forgives him for losing sight of the value of Blockbuster's life, but not for losing sight of the value of his own.