I'd be curious to know if there is a principled model for optimal human happiness which does not conflict so violently with our moral instincts.

Seems we need to take "creating" and "destroying" humans out of the equation - total or average happiness can work fine in a fixed population (and indeed are the same). We can tweak the conditions maybe, and count the dead and the unborn as having a certain level of happiness - but it will still lead to assumptions that violate our instincts; there will always be moments where creating a new life while making everyone unhappy or killing off someone to raise average happiness will be the right thing for the model to do.

I think we need to deal with "creating" and "destroying" people with other principles than happiness.