I enjoyed this overall, but I just want to point out that he didn't really make an argument against moral relativism, just said "practically, that's dumb." Most moral relativists [that I know] aren't so concerned with practice—they're instead trying to explicate that human sentient culture is just one possible variety of sentience in the universe. For example: if we could make exact copies of ourselves (incl. knowledge et all), would that be a good idea? Well, we have one moral viewpoint; the people we will be when we need to answer that question, though, will have different cultural biases—that is to say, context—than us. The universe has as many definitions of "good" or "bad" within it as there are ways to compose a utility function.