Our moral lives are rooted in our interests and our agreements. If we want to explain our moral lives, from gut-level moral perceptions to moral discourse intended to persuade others and ourselves, we need not go beyond very thisworldly interests and agreements. Hence morality is, broadly speaking, politics.
If morality is politics, it is ugly. It is not true that there are moral truths all rational agents must agree upon. This does not mean anything goes. But quite a lot things can go. Not every way of life is stable and successful in reproducing itself. But there are invariably many competing ways of life, which support different moralities, in our moral ecologies.
Attempts to provide a basis for morality, from stories about the will of the gods to sophisticated moral philosophies, are attempts to transcend politics. Interests and agreements are plural and fluid. Morality is something we care about very deeply, so it must be made more secure than that. It must be based on something higher.
One of the functions of discourse about the basis of morality, then, is to conceal the nature of morality.
To say that morality is partly concerned with concealment is not to deny that it is useful. Honesty and openness might be wonderful in an idealized academic context, but real human groups cannot function without deception. Our interests almost always demand a measure of concealment, deception, and coercion. Our moralities, because they typically condemn these as vices, allow us to make efficient social use of deception and coercion. It is best if our vital vices remain hidden.
Secular moralists are often very similar to their religious colleagues in this regard. Philosophers tend to retain many implicitly Capitalized superstitions even when they find no use for one of the old favorites, God. Chief among these is Reasonreason as something transcendent, rather than a useful cognitive tool.
Our moralities are all very thinly supported by reasons. It is more accurate to think of our moralities of having causes. These causes make who we are, including our interests and agreements, and hence our moralities. We can be reflective about our moral convictions. But there can be many different points of reflective equilibrium, even for wide reflective equilibrium. We still have a moral ecology, where many ways of life are stable upon reflection as well as other small perturbations.
An intellectually coherent scientific naturalism must come to grips with moral ecologies and moral pluralism. It must act against the desire to make morality transcend politics. By doing so, however, naturalism renders itself socially useless, perhaps even dangerous, in many contexts.