Yeah, I have similar ideas. On the other hand, rules that are Nash equilibria in the current "environment" are in some ways determined by the preferences of the (by now, long dead) agents (and even their initial bargaining positions). I'm having a hard time deciding how to categorize this kind of "morality" (if it can, in truth, be called such a thing). I ended up going with "Lean toward: moral anti-realism".