Raudhbjorn: I'm not saying there's no necessity, but that's getting sidetracked. I'm not talking about that at all.
I'm SPECIFICALLY talking about instances like this where you have a choice and you choose to kill instead. The MC is a good example of this. He chose to kill the demons because he understood there was no redemption and they would just keep killing (as you stated in your example). But in past cases like with the Holy Knights and Shera's brother, he chose not to (even though commentors felt they all believed he should) because he understood the weight of such actions, regardless of their twisted morality. These people did not deserve death, but these knucklehead commentors would relish in seeing Diablo in killing someone but if they were in his shoes they would have not killed them either.
That's what I'm getting at. You know the old saying about throwing stones in glass houses? Dunno about you, but I'm seeing a rain of rocks in here...