I'm just replying to the OP, not the replies because I haven't read them all.
Just because the bad guy I was fighting falls down doesn't mean that bad guy is dead. Now, my Katana scrapper for example, she's not hitting someone with the flat side of the sword (I saw this in a reply). That's just... no. If she were to do that, she'd carry a blunt weapon, not a razor sharp sword. Are the baddies surviving multiple slashes from her katana? No, probably not. Same with my Elec blaster. If they survive good for them, chances are they probably are not. My main, a MA/WP scrapper - yes. The baddies are probably just knocked silly and bent in that odd way (due to early ragdoll physics) but they're probably alive.
But are most heroes murderers in this game? Probably. However, murder is often justified depending on who and what the circumstances are. I'm not justifying it, but that's the way things are. It's more a reflection of human nature than anything IMO.