So if a society can rely on the sincerity of Epistemic virtue as a whole, then people can rely on it to bring benefits to the mass. If sincerity only has an instrumental value, then people can always abandon sincerity for their own personal interests. So that we have treated sincerity as something that we cannot abandon, and sincerity itself has values. So that we regard sincerity as a moral virtue is not because we ought to be moral from nowhere, but it is because to regard sincerity as a virtue by itself as a requirement of a stable society.