I'm really intrigued to see where this is going. Eliezer, you seem to be trending towards the idea that the "ought from is" problem is, if not solved yet, then solvable, and must and will be solved (in an urgent hurry!) to make FAI. Meaning, there will be a morality or meta-morality built on rigorous math and as unarguable as Bayes. It will be genuinely right, and everyone else will be genuinely wrong. Whole religions, cultures, and political movements will become provably, mathematically false.

I think you might make some enemies ;-)