ADVANTAGE: EVOLUTIONARY STABILITY.

Richard Cocks takes on the social constructivists.  "Evidence that moral thinking is not a 'social construct' can be shown further by pointing to elements of morality that are demonstrated in the animal kingdom."  His example is more about envy than it is about justice, but it's more straightforward to observe that young animals that behave in too unmannerly a way are the ones most likely to be killed and eaten.  Mannerly behavior, including grooming and sharing, confers evolutionary advantage.

So, too, with more complicated conventions.

I have had success in getting students to agree that the Holocaust was immoral, that female genital mutilation is immoral, that slavery in other cultures is immoral. Some students express the concern that for changing their beliefs in these ways, they will be judged racist and immoral by their contemporaries. But that is a risk that all moral realists must face.

Yes, in the same way that the use of evolutionary stable strategies confers evolutionary advantage on adopters, the non-use leads to outsiders and Othering.