While such an extreme scenario is, needless to say, unlikely, the idea of centralizing the majority of social media under the control of a government that has shown increasing interest in mass surveillance remains something I am exceedingly dubious about.
I also believe that such a platform is the quickest path towards incorruptible technocracies, slowly but surely through referendums being opened up through the platform (small, local decisions at first).
If this does not occur in the public sector, then I view governments as the taxi industry to capitalism's uber, and it will be the free market (controlled by increasingly intelligent public demand more than lagging legsislation) that starts to provide more 'pure democracy' behaviors. (As an aside, I wonder whether we shall start to see more interestingly structured IPOs)
The cynic in me sadly suspects that socialism just isn't fast enough, and that the free market will be the dominant tool for change - But that slowly but surely, public voice will become a more ethical one - In this era we are in which is surely a second age of enlightenment. Hopefully this will sculpt the free market to be more aligned with the commons, and less brutally and bluntly aimed at collecting $.
the "Best Korea" has the fastest socialism in the world - heck it even has its own "social networking platform"
...and it's also "democratic" (in its own way, of course)
And that implies we can't solve the issue with technology alone. Moderation needs to be possible, but we have to figure out a way to prevent abuse.
Disruptive users do get shadow-banned, but it's trivial to create new ones. With accumulating karma, there is some pressure to self-censor. But overall, I like it better than StackExchange or reddit, for example.
Edit: I just noticed that this submission about Bitcoin energy use has been raised from the dead: https://news.ycombinator.com/item?id=16498776
I do agree with your thesis that we need social platforms immune to arbitrary censorship, however.
I think the solution is some sort of trustless P2P system, where no one entity exercises ultimate control, and censorship is impossible, or at least very difficult. Of course that means that the platform won't be beholden to any nation's laws, irrespective of whether those laws are, in my opinion, just (criminalizing distribution of child pornography, for example) or not (criminalizing open political dissent, for example).
However, if I have to choose between absolute free speech and government- or megacorp-controlled, surveilled, and mediated social interaction, I choose absolute free speech.
Most major social media collaborate so well with their country's elites, governments and national interests, that they might as well be run by their state.
Instead of run by the state, governments could choose to give out vouchers redeemable only at social platforms that charge users directly for their services instead of relying on the advertising and data-sales game.