Moral relativism defended

My thesis is that morality arises when a group of people reach an implicit agreement or come to a tacit understanding about their relations with one another. Part of what I mean by this is that moral judgments - or, rather, an important class of them - make sense only in relation to and with reference to one or another such agreement or understanding. This is vague, and I shall try to make it more precise in what follows. But it should be clear that I intend to argue for a version of what has been called moral relativism.