I'm with you for almost all of that journey. Companies should be held accountable for their actions. There are consumer protection laws, and I think it's reasonable for those laws to include protection against things like automated takedowns with no appeal process.
I just can't quite go as far as to say that Google or Facebook should be treated as governmental entities. The bill of rights restricts what government can do. It has never been interpreted as restricting what an individual person can do, even if that person heads a giant corporation.
Solve these problems another way, not by literally nationalizing social media.
My point is censorship is a huge responsibility and power, especially when it is done at the scale govts and multi-national corps do, and therefore it needs serious transparency and checks and balances, in both cases.
I don't see this happening to satisfaction. Instances of regrettable censorship stay regrettable, and keep recurring.