This is a linkpost for https://opinionator.blogs.nytimes.com/2011/07/24/the-maze-of-moral-relativism/
Actually, I don't know if you and Boghossian really disagree here. I think Boghossian is trying to argue that your normative preferences arise from your opinions about what the moral facts are. So I think he'd say:
IEPB: "People ought to do X" is your preference because you are assuming "People ought to do X" is a moral fact. It's a different issue whether your assumption is true or false, or justified or unjustified, but the assumption is being made nevertheless.
For example, when you exhort IEPB to not make mediocre philosophy arguments, and say that that's your preference, it's because you are assuming that the claim, "philosophy professors ought not to make mediocre philosophy arguments", is in fact, true.
IEPB: "People ought to do X" is your preference because you are assuming "People ought to do X" is a moral fact. It's a different issue whether your assumption is true or false, or justified or unjustified, but the assumption is being made nevertheless.
If my mental model of moral philosophers is correct, this contravenes how moral philosophers usually define/use the phrase "moral fact". Moral facts are supposed to (somehow) inhere in the outside world in a mind-independent way, so the origin of my "People ought to do X...