I must admit that my preference to save a person from drowning-actually is no better than a preference to save a person from drowning-virtually. It happens that I have the former preference, but I'm afraid it is incoherent.

It's better, because it's what your preference actually is. There's nothing incoherent about having the preferences you have. In the end, we value some things just because we value them. An alien with different morality and different preferences might see the things we value as completely random. But they matter to us, because they matter to us.