You have a good point. But there is a difference between people who see killing others as a regrettable last choice (e.g. in self-defence), and those who see killing others as "no big deal" (sociopaths, and their happy-death-spiralled followers). Although there probably is a continuum.

EDIT: The difference is that a non-sociopathic utilitarian considers a possibility of running on a corrupted hardware, if they are a rationalist, or simply deflect the thought by an "ugh field" if they aren't.