There is a certain security risk to an online ID but ones that can be mitigated in the same way people's bank accounts, for the most part, are kept safe. I would also argue that it should be an impartial international body not a state one that would oversee it. The internet and these large social platforms are the global public sphere, they are the modern coffee shops and that requires cross border oversight but not interference in what people can say. Yes there are huge challenges to achieving that, consensus being the big one. The reason I think blockchain is useful here is that we can create an immutable global database, people will need to keep their keys safe in the same way we keep passports, house keys and accounts safe. We need to up the cost of creating fake accouts or bot accounts. Fabricating a person is hard and expensive, the same rules need to apply online.
I agree with everything else you have said except the last point and maybe the disinformation police, that is a slippery slope. What constitutes a conspiracy theory or disinformation? Who makes that decision? Yes blantant lies can be caught but other areas are very grey. The public sphere is the best mechanism for this but without accountability and a lock down on account creation we cannot have a true digital public sphere.
