First, thank you for a clear exposition on a complex topic. I thought you might find interesting an 'ought' from 'is' that I stumbled upon.

It is an ethic that follows from an observation within material existence (which I got from Warren J. Samuels): human beings have no choice but to effect choices. Therefore, choosing for ourselves is integral to human being. Therefore we are required to respect one's another's capacity to choose — beginning with choosing whether, how. and to what extent to be involved whenever any choice is being effected.

To do that is to acknowledge one another as fellow human beings; to act otherwise is to assert by one's action (which must necessarily take place within material existence) some status regarding 'thee and thou' that cannot be verified within material existence.

That's the key: since both the determiners and the referents of this ethic are located within material existence, that legitimately de-legitimates going outside material existence (to beliefs) to deny the applicability of the ethic to oneself.

So this ethic is 'mutual respect in effecting choices'. Its applicability is limited to actions related to effecting choices that involve other human beings. Outside that domain we are left with personal morality.

To distinguish it from morality I call this ethic the ethic of justice. The ethic and its implications together I call 'real justice'.

Anyway, I just thought you might find it interesting. If you did want to see more about its implications, there is "Real Justice (summarized for a '5 min read')" here in Medium.