Different models for different cases, right? It's only a counterpoint if one believes that the message is "federate everything."
There is no privacy guarantee in federated systems. There's no privacy in public forums, full stop; nor should there be any expectation of any. You can barely achieve any privacy trust in 1:1 communications, and much less any form of many-to-many.
Anonymity is another matter - you can have anonymity, if you're careful, but privacy? No. Federation is not about providing privacy, or even anonymity - there's no section either in the AP specification.
For private communications, you use different technologies; P2P is a good option, but you can get privacy and anonymity in federated systems like Nostr, which - while capable of being a public forum - has all the parts needed to achieve anonymity and privacy.
Tox has a good model which they can't seem to get to work. 0xchat is interesting.
It gets said repeatedly: you tailer your solution to your threat model; there's one size fits all.