Mow...your logic is absolutely rediculous. You sound just like the usual bleeding heart liberal who always villafies the innocent victim.
There is no way in hell the guy could have known whether the robber was armed with a gun or a knife...and if I was in the guy's position of being robbed and had already been knocked onto the ground with a pipe or whatever to the back of my head I am not going to sit there and play pansy-as* with the perp to see what's next. I'm going to end it there and now.
I'd rather take my day in court than to wait until I take a bullet to my head or get my head bashed in with the pipe by somebody who has already crossed the lawful line to begin with.
If you carry any firearm you might as well just forget about carying it because if this situation happened to you, you are probably going to end up being wasted because you are sitting there guessing with yourself whether or not the attacker is going to kill you or not. That's stupid man...just plain stupid.