If we ask:  “Why ought I to be unselfish? And you reply ‘Because it is good for society,” we may then ask, ‘Why should I care for what’s good for society except when it happens to pay me personally?’ and then you will have to say, ‘Because you ought to be unselfish’—which simply brings us back to where we started.  C.S. Lewis

Explaining why you WANT people to act morally is one thing.  Explaining why they SHOULD is another.