Self-defense during a mugging is often justified because the victim was uncertain as to the intentions of the criminal.
“Will he kill me even if I give him my wallet? What if he gets upset and shoots because I only have $20? What if he decides that I’d be able to identify him? What if he’s just crazy?”
Suppose now that you are somehow 100% certain that if you surrender your money, then the mugger definitely will not kill you; and just as certain that if you resist, then he will try to kill you.
Then if you resist, either he kills you or you kill him. Either way, a “killing” will occur. On the other hand, if you submit, then only a “stealing” will occur. But any utilitarian will tell you that a killing is worse than a mere act of theft. If only consequences matter, isn’t it your moral and perhaps even legal duty to part with your cash?
This argument is both invalid and unsound.
It is invalid, because think of the message this kind of “social contract” will send to potential future muggers. “Oh, so all I have to do to get loot with no danger to me whatsoever is to convince my victim that if he gives me all he’s got, then I’ll definitely spare his life? I’m sure ways of doing so can be devised.” This’ll make mugging a much more attractive profession, sharply upping the crime levels. And why stop there? A guy with a shotgun orders you to squeal like a pig. Isn’t “someone got killed” still a situation inferior to a “someone got raped in the ass” or even “someone got severely maimed / paralyzed”? A utilitarian must take these points into account.
It is unsound, because the victim is deontologically and according to common-sense morality (rather than perhaps the highly controversial utilitarianism) within his rights to choose the course of action. He is permitted to submit, and he is permitted to resist. If he chooses the latter, then we have a straightforward shooting in self-defense. Instead of “stealing” vs. “killing,” we need to compare “unjust stealing” and “justifiable killing.”