I read it as a warning about expecting sufficiently rational beings to automatically acquire human morality, in the same way that sufficiently rational beings would automatically acquire knowledge about true statements (science, etc). The lesson is that preferences (morality, etc) is different from fact.

I agree that is what it is trying to say, but...as you made illustrate above..it only appears to work if the reader is willing to bel fuzzy about the difference between preference and moral preference.

If you want to know Eliezer's views, he spells them out explicitly

For some value of "explicit". He doesn't even restrict the range of agents to rational agents, and no-one expects irrationali agents to agree with each other, or rational ones.

To me, "No universally compelling arguments" means this - two rational agents will converge upon factual statements, but they need not converge upon preferences (moral or otherwise) because moral statements aren't "facts".

Mathematical statements aren't empirical facts eitherl but convergence is uncontroversial there.

It really doesn't matter if you define the pebble sorting as a "moral" preference or a plain old preference.The point is, that humans have a morality module - but that module is in the brain and not a feature which is implicit in logical structures, nor is it a feature implicit in the universe itself.

Are you quite sure that morlaity isn't implicit in the logic of how-a-society-if-entities-wth-varying-prefernces manage-to-rub-along ?