[The words "his" Bruce said to Jason during their last fight still ring in Jason's mind]

I asked him if he couldn't do it because it's too hard to cross that line. He said "it'd be too damn easy." He said all he ever wanted to do was subject the Joker to every torture that monster has inflicted and then kill him. But what's stopping him is that he believes if he goes down that road, he'll never come back.