Isn't the giant elephant in this room the whole issue of moral realism? I'm a moral cognitivist but not a moral realist. I have laid out what it means for my moral beliefs to be true - the combination of physical fact and logical function against which my moral judgments are being compared. This gives my moral beliefs truth value.

That leaves the sense in which you are not a moral realist most unclear.

And then strangest of all is to state powerfully and definitely that every bit of happiness must be motivating to all other minds, even though you can't lay out step by step how the decision procedure would work. This requires overrunning your own claims to knowledge in a fundamental sense - mistaking your confusion about something for the ability to make definite claims about it.

That tacitly assumes that the question "does pleasure/happiness motivate posiively in all cases" is an emprical question -- that it would be possible to find an enitity that hates pleasure and loves pain. it could hover be plausibly argued that it is actually an analytical, definitional issue...that is some entity oves X and hates Y, we would just call X it's pleasure and Y its pain.