What seems to be overlooked in most discussions about total hedonistic utiltiarianism is that the proponents often have a specific (Parfitean) view about personal identity. Which leads to either empty or open individualism. Based on that, they may hold that it is no more rational to care about one's own future self than it is to care about any other future self. "Killing" a being would then just be failing to let a new moment of consciousness come into existence. And any notions of "preferences" would not really make sense anymore, only instrumentally.