On the basis of utilitarian notions of right and wrong, I would have no issue with saying that Bob is objectively wrong- he disagrees with what I claim is objectively right. If all I had were preferences, I could no more claim Bob was wrong to prefer to be a murderer than I could claim he was wrong to prefer to be an art teacher. I say, 'I wouldn't do that if I were you', he replies, 'Good thing you're not!', end of discussion. And then I guess he would probably murder me. Or worse: teach me art.
Faith also beats preference here in that, given the premise that it is good to reduce suffering and increase happiness, I arrive at the same conclusions about morally correct actions regardless of the time and place that my mind happens to exist in. I can align my actions to the right choice even if I was raised to prefer something else. A slave owner prefers that slavery exists; a utilitarian slave owner can see that that is wrong and free their slaves.
Faith also beats preference here in that, given the premise that it is good to reduce suffering and increase happiness, I arrive at the same conclusions about morally correct actions regardless of the time and place that my mind happens to exist in. I can align my actions to the right choice even if I was raised to prefer something else. A slave owner prefers that slavery exists; a utilitarian slave owner can see that that is wrong and free their slaves.