Moderation is not authoritarianism.

If you use moderation as a tool to push your ideology, sure it is.

If your ideology is printed in the rules before you enter, and you agree to respect those rules before entering, and the rules are things like "don't target individuals with racism, transphobia, homophobia, etc" it's really not authoritarianism.

I can't yell in a library, the librarians aren't authoritarian. I know going in that libraries aren't the place for that.

Except Twitter does allow racism against whites. So its rules are not “don't target individuals with racism”, but “don't target non-white people with racism”, which sends a clear ideological message. Same with other demographics.