One other things:
> "You don't need to believe that your system is "correct" in some sort of universal way. You merely need to believe that your system will be best for your personal interests."
Relativism is not egoism.
Right or wrong have absolutely nothing to do with it. It can't, because without a universal morality any notion of universal "right" or "wrong" evaporates. This is about refusing to tolerate another culture not because "it is wrong" but rather because it is beneficial to you to do so.
Your problem here is that you seem to be assuming some sort of universal "respect the right of others to coexist" or "live and let live" morality, where you should not stamp out other cultures unless you have determined that they are "wrong". This sort of universal tolerance for other systems of morality does not exist. It really simply doesn't; history would be far less bloody if it did.
People that do not believe in universal morality are still very capable of acting only in their own best interests, at the expense of others. Egoism is not incompatible with moral relativism.
How so, as long as you accept that those meta-judgements are still subjective?
So a moral relativist can say something like "I dislike your approval of female genital mutilation", but this is not a claim about the rightness or wrongness of the approval of female genital mutilation. It is instead a claim about their own sentiments. This is just like saying "Well I don't like sushi" in response to a friend saying that they like sushi. You'r not saying that them liking sushi is wrong.
Or to put it in another way, meta-ethical moral relativism doesn't require normative relativism.
So it's not uncontroversial to say that you can be an objectivist moral relativist. In any case, this discussion has been about metaethical relativism.