Except if that were the case why hasn't JASON killed the Joker by this point? Trying to make Batman do it is past "necessity" and into "ludicrous" Good point, he kind of has a Proffesor Zoom thing going on with Batman doesn't he?
Still, I take that as the exception, since as he says in the scans it was more personal with Joker, as opposed to the drug dealers and gangsters he killed earlier in the story, as well as taking down Mr Freeze.
But really, this part of the story, while pretty awesome with what Jason is saying to Batman, is where the story sort of leapt off the tracks. The preceding parts had better art and cooler Jason.