Well sure, but note that “depriving someone of their liberty/autonomy IRL” is not the only form of authority. Your boss has authority over you, and they can abuse that authority in all sorts of ways that don’t amount to deprivations of liberty or autonomy.

Besides, the “how do we police online communities” question is a clear analogue to the “how do we police IRL communities” question. Fundamentally you’re talking about what behavior is acceptable, who decides what’s acceptable, and how the community responds to unacceptable behavior. If you can’t even run an online community without having an unelected person unilaterally banishing people over vague, changing rules that aren’t up for a vote, how are you supposed to run a real community without any form of authority?

The simple answer to all this is that while authority should have to justify its existence, if its existence is justifiable then that authority is allowed. This is still a fundamentally anti-authority position; it’s just not dogmatic about it. It’s like the difference between strict pacifism vs. opposing violence except as a last resort.