First, thanks for an intelligent essay on the most important topic always confronting humanity.

Warren J. Samuels all but defined "social power" as the ability to effect choices (choose among perceived alternatives and take action to bring that choice to fruition). ["Welfare Economics, Property, and Power" in Perspectives of Property, Gene Wunderlich and W. L. Gibson, eds. (1972)] As individuals and as groups, such as societies (including geopolitical communities), human beings have no choice but to effect choices.

That makes choosing integral to being human. That gives us a starting point within material existence for an ethic of justice that is universal and eternal (as long as human beings continue to have no choice but to effect choices): all must respect the capacity of all other people to choose, beginning with choosing whether/how/to what extent to be involved whenever any choice is being effected.

It boils down to a handful of absolute prohibitions: no killing, harming, coercing, stealing, or manipulating (which includes lying, cheating, etc.) in relations with other human beings in actions undertaken (including speech acts) to effect any choice. Those apply for any choice, whether for oneself or on behalf of any other person(s), group, organization, cause, etc.

If curious for more, a "2 min. read" basically repeats what was written in this Reply, but has links for more about this approach to justice at the end of it: "Can't Get Any Simpler" (here in Medium but not behind the paywall).