Wei_Dai:

If it's 2, why do we think that two people on opposite sides of the Earth are referring to the same complicated blob of values when they say "morality"? I know the argument about the psychological unity of humankind (not enough time for significant genetic divergence), but what about cultural/memetic evolution?

You don't even have to do any cross-cultural comparisons to make such an argument. Considering the insights from modern behavioral genetics, individual differences within any single culture will suffice.