Vaniver, I really appreciate the rigor you are bringing to this discussion. The OP struck me as very deliberative-utilitarian as well. If we want to account (or propagate) for a shared human morality, than certainly, it must be rational. But it seems to me, that the long history of searching for a rational-basis-for-morality clearly points away from the well trodden ground of this utilitarianism.

From Plato and Aristotle to the Enlightenment until Nietzsche (especially to the present day), it seems the project of accounting for morality as though it were an inherent attribute of humanity, expressible through axioms and predetermined by the universe, is a bunk and, perhaps even, an irrational project. Morality, I think can only be shared, if you have a shared goal for winning life.

A complete description of values requires a discussion on what makes life worth living and what is a good life, or more simply goals. Without the tools to determine and rationalize what are good goals for me, I will never be able to make a map of morality and choose the values and virtues relevant to me on my quest.

Does that jive?