What I think is a far more likely scenario than missing out on the mysterious essence of rightness by indulging the collective human id, is that what ‘humans’ want as a complied whole is not what we’ll want as individuals. Phil might be aesthetically pleased by a coherent metamorality, and distressed if the CEV determines what most people want is puppies, sex, and crack. Remember that the percentage of the population that actually engages in debates over moral philosophy is diminishingly small, and everyone else just acts, frequently incoherently.
(Just not all at the same time.)