OK, bad choice of words.

No, but you need some decision theory to go with your utility function, and I was considering the possibility that Parfit merely pointed out a flaw of CDT and not a flaw of common sense morality. However, given that we can still think of situations where common sense morality (no matter the decision theory) executed by everyone does predictably worse for everyone concerned than some other theory, Parfit's objection still stands.

(Incidentally, I suspect that there could be situations where modifying your utility function is a way to solve a prisoner's dilemma, but that wasn't what I meant here.)