Sure, they believed that the bourgeois value system functioned to maintain the bourgeois status quo (isn't that true?). But you seem to be saying that disagreeing with the bourgeois value system is a moral anti-realist position.
They believed that the concept of morality itself was merely a tool of oppressors, or at best merely a tool that they might as well turn against the bourgeois.
Inside view vs. outside view.
From Being a Realist (even if you believe in God):
My mother, who doesn't call herself a theist (I think she's agnostic), doesn't even accept realism. She doesn't even agree with this:
That's little more than tautologies here. Yet it elicited an impression of being forced to believe. I know because she told me about the totalitarian dangers from such narrow thinking.
I'm happy to have finally found the root cause of our ongoing disagreement, but now, how can I deal with that? It looks pretty hopeless, but just in case, does someone have a suggestion, or should I just leave it at that? (My ego doesn't like it, but giving up is an option.)
Now I'm relieved to know that in near mode, she's a complete realist. This craziness only shows up in far mode.