[blakdawg]

If your quibble is with the idea of a "protected group", his language is very close to that of a well-established term, "protected class" that's familiar to anyone working on the legal side of anti-discrimination.

The idea itself certainly isn't one he made up - the idea that it's possible to sort people into different groups based on physical or conceptual criteria is probably older than language. It's also one that "marginalized people" or "historically oppressed groups" (or whatever label you prefer) also struggle with.

I don't know if there's a generally accepted definition of "social justice", but one of the core concepts seems to be concerned with identifying and correcting privileges and oppressions (e.g., injustices) which are enjoyed or visited upon people based on their (perceived) membership in social groups.

There's nothing unreasonable about asking for clarity about which groups fall into the "oppressor" and "oppressed" categories; and about how group membership is determined. Even within "social justice" movements, there are complicated questions about that - e.g., trans people, Rachel Dolezal, etc.