But if you mean it's some simple fact that we're morally obligated to restrain ourselves from doing certain things, no. Or at least I don't see how that could even possibly be the case, and I already have a theory that explains why people might mistakenly think such a thing is the case (they mistake their own values for facts woven into the universe, so hypothetical imperatives look like categorical imperatives to them).

Well, I have a theory about how it could be the case. Objective morality doesn';t have to be a fact-like thing that is paradoxically indetectable. It could be based on the other source of objectivity: logic and reason. It's an analytical truth that you shouldn't do to others what you wouldn't want done to yourself. You are obliged to be moral so long as you can reason morally in the sense that you will be held responsible.