Again, if the question for moral universalism were, “where do all peoples agree on values” we’d have an empirical answer, but still not a philosophical answer. In any case, the empirical answer would still be forthcoming. All peoples do recognize certain principles of fairness, among other notions that motivate them. Most (all?) global religions hold to principles that stand in stark contrast to purely selfish interests. Morality is universal and is universally of a kind, even when it isn’t exactly alike.
Overall, notions of both morality and mores contrast pure self interest, which is odd, since our species nature includes both selfishness and altruism. Yet mores and morality do not try to contradict altruism. The basic notion of morality seems always and everywhere a negotiation with selfish interest where self interests might lead to conflict.
One way to define morality is that contrast: morality is not just a consideration of agent action, but consists of precepts beyond the natural, instinctive desires of self-interest. Agentive actions motivated by self interest need no precepts; they take care of themselves. Morality — and mores — concern the agent beyond the agent’s own natural compulsion.
That’s why morality always seems so anti-Nietzschean and anti-power. But Nietzsche misperceived and exaggerated. No doubt morals will appeal to the slavish spirit, but they do not originate from it. It is the nature of morality to promote something else besides natural inclinations, because a) natural inclinations need no such promotion and b) altruistic inclinations don’t conflict with other interests directly. That leaves the self-interests that do conflict with others’.
Here’s an empirical test: strip away all the mores and see what’s left in morality. I think you’ll find that there is still a variety of notions that might be described as moral. There’d be the sentiment expressed, for example, in “You did x, so why shouldn’t I?” (“Everybody does it, why shouldn’t I?”) There’d be a notion of fairness deriving from our species ability to see ourselves in others’ situation — empathy, a basic character of humans. There’d be a bunch of general precepts beyond mores: haste makes waste, bird in hand’s better than two nearby…all sorts of modulations and tempering of immediate selfishness.
That’s the stuff of morality. That’s where it begins. While it’s true that there is no universal agreement on a complete and consistent set of moral precepts, it’s also true that wherever you look, peoples, religions, cultures, laws, all regard this tempering morality as fundamental.
There’s no question that morality is universal, empirically. You can see it in the exception that ‘proves the rule’, the sociopath. The sociopath is identified as abnormal and psychologically exceptional primarily on account of not having a moral sense at all. Sociopathy defines the normal human as moral — moral and not just following local mores. Sociopaths follow the local mores. They dress well, talk well, behave better than well — they are notably expert at sociableness. The sociopath is the most beguiling person at a party, and will charm your pants off. They’re not defective in mores. It’s their moral character that is distinctive. It’s missing, and apparently not by choice, but by some strange character of their minds. (I’ve known at least two well, and they are the most fascinating people — exciting because they will do all the things you and I won’t.)