YES! I think this is exactly right: moral realism is not at odds with the orthogonality thesis; but the conjunction of moral realism with moral internalism is.

And it is this conjunction that many people seem to believe, although I cannot see why, because I can't even imagine what it would mean for the world to be such that it is true. So I find it obvious that the conjunction isn't true. It's not quite so clear which of the conjuncts is false (if not perhaps both), though.