Corporations censor speech and any content in their platforms that they deem undesirable or threatening to their profits. That’s totalitarianism by definition, and yet private.
Public discourse squarely belongs to the public, and hosting it must be perceived and intended to be a kind of public service; otherwise we can just go back to the good old days of gathering and debating in public squares.
Totalitarianism would require the government to do the censoring.
You can't assume the government wouldn't censor based on the exact same criteria.
An entity with control will exercise it.
When it's a private entity there's a theoretical other place you can go. When it's public (government) there is fundamentally no other place you can go.
Government isn’t the only entity capable of public service. Non-profit organizations are a thing. And that is precisely why the comment I replied to has problematic notions of “public” and “private”. NPOs are private entities, but do not behave the same way as corporations.
