I think there’s a misunderstanding here: anonymous means you can’t know who wrote what, which does enable extreme voices. What you’re talking about is pseudonymous speech.

Assuming people don’t use multiple accounts and don’t share accounts with others, the current state of Twitter and all major social networks is pseudonymity, not anonymity: you know that all tweets by @someone were written by the same person. Their "real" name doesn’t matter as long as they always use the same pseudonym.