If someone pulls a gun on you and demands your wallet, how do you know whether his intent is to merely threaten you or to do you harm? Benefit of the doubt is one thing but when your life is in the balance you need to be a bit more cynical about the other guys intentions. How neccesary his death would be is an endless theoretical debate. The guy may never do another crime after getting your wallet or he may become ever more emboldened to more violent crimes....crimes you might have prevented. It's really a shortsighted argument to not think beyond the immediacy of whether you give up your wallet or not. I'll assume the worst, plug the sh**head, and take my chances with the maker later on.
As I said before, it's a personal choice. Good luck living with yours.

Ed