Oh well in that case, we disagree about what reply we would hear if we asked a friendly AI how to talk and think about morality in order to maximize human welfare as construed in most traditional utilitarian senses.

This is phrased as a different observable, but it represents more of a disagreement about impossible possible worlds than possible worlds - we disagree about statements with truth conditions of the type of mathematical truth, i.e. which conclusions are implied by which premises. Though we may also have some degree of empirical disagreement about what sort of talk and thought leads to which personal-hedonic results and which interpersonal-political results.

(It's a good and clever question, though!)