I think your interpretation oversimplifies things. He's not saying "morality is an inborn or taught bland desire to help others"; he's rather making the claim (which he defers until later) that what we mean by morality cannot be divorced from contingent human psychology, choices and preferences, and that it's nonsense to claim "if moral sentiments and principles are contingent on the human brain rather than written into the nature of the universe, then human brains should therefore start acting like their caricatures of 'immoral' agents".