First, thanks to this author for this very informative article.

As to the quote, I would agree that just governance does require a universal ethic. Any belief (as to right/wrong, good/bad, just/unjust) could be universal, but none ever has been, even within any single society (within civilization, anyway). An ethic following from an observation within material existence, the validity of which all people can verify for themselves, would be just that. Hume, along with every philosopher (or theologian) ever, assumed such a thing could not be. (Marx claimed to eschew any ethic based on belief, proclaiming himself to be a materialist, but he was really, I maintain, a radical equalitarian.)

I am convinced I have found such an ethic: a requirement of mutual respect (taking one another into account as we live our separate lives together in this world) following from the observation that human beings have no choice but to effect choices (which I got from Warren J. Samuels). If curious, there is "Beyond Liberalism" (here in Medium).