right, but I don't think we can ignore the problem of cesspools of really toxic behaviour that is at times enabled with anonymous handles. Moderation is much more important in those contexts. HN works because it's pretty heavily moderated (both by users via downvotes + comments and admins).
But a heavily moderated forum is not a completely free discussion environment. And the forums full of toxic comments aren't really that free either, because a huge portion of potential participants choose not to participate because of the nasty environment.
Clearly in some (many?) contexts there's a need for anonymity, and in some cases (HN) it seems to work out ok. I'm just not sure if anonymous is the right default for a lot of social media contexts. Both Slashdot and Reddit have become unusable for me because of the signal to noise ratio is so low (reddit may have some subreddits with better behaviour, but not any of the ones I found personally interesting).