Lessons from usenet: a social group can thrive on reputable pseudonyms. It can't have discussions at all if it responds to anonymous people.

If you can use TOR (or some similar system) to send messages which are authenticated to a consistent pseudonym, that's good. If you can send unauthenticated messages, that's bad.

Maintaining N pseudos by default ought to be easy and client-side: "Select the account to post this from:" [professional] [community] [friends] [family] [...]