I don't know about the Nash equilibria, but I agree with most everything you've written here. I'd just prefer to call that (quasi-)universal subjective ethics, and to use language that reflects that, as there are exceptions - call them psychopaths or whatever, but in the interest of accuracy. And the other problem with the objectivist interpretation of custom is that sometimes customs do have to change, and sometimes customs are barbaric. It seems that what you were getting at with "actually wrong" in your initial post was the idea that these kind of moral sentiments are universal, which I can buy, but even that is a bit of a leaky generalization.