The good point that I like that Dick makes here is "We're not soldiers. We're not cops." Because either one could kill. A cop could take out the Joker and it would be totally legitimate. Then planning to go out, catch him and kill him would be a major line-crossing, I think. It sounds silly, but I really think they're right about that, in terms of their own psychology.
But more importantly, wtf with Dick's hair? It's the kind of 'do I'd expect on a supervillain.
Btw, is Dick the only one of them that actually has killed? I mean, he kills the Joker in--is it in this story? And Batman brings him back. And while he didn't kill Blockbuster he did seem to run out of reasons not to keep him alive. That is, I can see how he thinks of himself as killing him.