I can see why you disagree w/ grandparent, but please note that CEV isn't supposed to be a grand new ethical theory. Somewhere in the background of 'why do CEV rather than something else' is a metaethical theory most closely akin to analytic descriptivism / moral functionalism - arguably somewhat new in the details, arguably not all that new, but at any rate the moral cognitivism part is not what CEV itself is really about. The main content of CEV looks like reflective equilibrium or a half-dozen other prior ethical theories and is meant to be right, not new.