This is a helpful clarification. "No universally compelling arguments" is a poor standard for determining whether something is objective, as it is trivial to describe an agent that is compelled by no arguments.

It's a poor standard for some values of "universal". For others, it is about the only basis for objectivity there is

. But I think people here use it as tag for a different argument: that it's totally unclear how a Bayesian reasoner ought to update moral beliefs, and that such a thing doesn't even seem like a meaningful enterprise. They're 'beliefs' that don't pay rent..

They're beliefs that are difficult to fit within the framework of passively reflecting facts about the world. But fact-collection is not an end in itself. One eventually acts on them in order to get certain results. Morality is one set of rules for guiding action to get the required results. it is not the only one: law, decision theory, economics, etc are also included. Morality may be more deniable for science types, since it seems religious and fuzzy and spooky, but it remains the case that action is the corollary of passive truth-collection.