First of all, thank you for that article. There is a feast of substantive food for thought in it.

I thought you might find interesting the 'ought from is' I happened upon. As any such ethic must be, it is 'scientific' in the sense that it follows from observation within material existence. So anyone who accepts the validity of the observation must accept the applicability of the ethic to all human beings, including oneself.

The observation (which I got from Warren J. Samuels) is that human beings have no choice but to effect choices. The ethic is mutual respect in effecting choices (i.e. respecting one another's capacity to choose, beginning with every person’s choosing whether/how/to what extent to be involved whenever any choice is being effected). To abide by the ethic is to recognize others as fellow human beings; to act otherwise is to assert by one’s actions some status regarding oneself and any other being(s) involved that cannot be verified within material existence.

So actions (which take place within material existence) that involve other human beings in the process of effecting any choice comprise the domain of justice. Those actions are the sole concern of justice (not motivations, intentions, etc.). Since both the determiners and the referents of the ethic are located within that existence, going outside it (to beliefs, emotions, conjectures, etc.) to refute or ignore the ethic is legitimately de-legitimated. Outside the domain of ‘real justice’ (as I have come to call it), morality (which is always belief-based) takes over.

If curious, there is "Real Justice (summarized for a '5 min read’)" here in Medium.