Concerning preferences, what else is part of morality besides preferences?
"Inseparably Right" discusses that a bit, though again, I don't recommend reading it out of order.
What is debated is whether anything else can justify should or ought statements. Can categorical imperatives justify ought statements? Can divine commands do so? Can non-natural moral facts? Can intrinsic value? And if so, why is it that these things are sources of normativity but not, say, facts about which arrangements of marbles resemble Penelope Cruz when viewed from afar?
These stand out to me as wrong questions. I think the sequence mostly succeeded at dissolving them for me; "Invisible Frameworks" is probably the most focused discussion of that.
I do take some confort in the fact that at least at this point, even pros like Robin Hanson and Toby Ord couldn't make sense of what Eliezer was arguing, even after several rounds of back-and-forth between them.
But I'll keep trying.
In You Provably Can't Trust Yourself, Eliezer tried to figured out why his audience didn't understand his meta-ethics sequence even after they had followed him through philosophy of language and quantum physics. Meta-ethics is my specialty, and I can't figure out what Eliezer's meta-ethical position is. And at least at this point, professionals like Robin Hanson and Toby Ord couldn't figure it out, either.
Part of the problem is that because Eliezer has gotten little value from professional philosophy, he writes about morality in a highly idiosyncratic way, using terms that would require reading hundreds of posts to understand. I might understand Eliezer's meta-ethics better if he would just cough up his positions on standard meta-ethical debates like cognitivism, motivation, the sources of normativity, moral epistemology, and so on. Nick Beckstead recently told me he thinks Eliezer's meta-ethical views are similar to those of Michael Smith, but I'm not seeing it.
If you think you can help me (and others) understand Eliezer's meta-ethical theory, please leave a comment!
Update: This comment by Richard Chappell made sense of Eliezer's meta-ethics for me.