There is a significant difference. Facebook is a private business that has rules, if you break the rules then your post, or eventually your account, gets canned. Now, given the USPS is a government run entity, if they refused to send out your mailshot because they disagree with the message, then that would be a breach of you First Amendment rights. Verizon is another private company.
These people have been "deplatformed" not because of who they are (your claim), but because of what they said. Constitutional rights are not without limits. Free speech is not without limits and certainly has consequences.
Were you as concerned when the GOP controlled both houses during Trump's first two years?
Who's "they"? It's certainly not the Democrat Party. Seems like it's a few citizens exercising their constitutional right to free speech in expressing their dislike of Ngo's book. You support that, presumably? Just like you presumably support the right of a christian baker to not serve gay customers? For the record, the book store should, IMHO, be able to stock any book it wants. It may not be good business in the long run, but it should definitely be their decision. If you don't like that as a customer, then you have the freedom to buy your books from another store.
You are correct. YouTube and Facebook should have the right to censor content. As a result they should lose the government protection that prevents them for being sued for any defamatory content they allow to remain on the site. They're either a publisher or a platform. Can't be both.
Of course you can have both. The fix would be putting a time limit on the protection, i.e. 24 hours after learning about a ToS violating is known to them it is either deleted or they become liable, as they otherwise have to censor ALL content before it becomes visible. That would give them, by forcing them, the absolute control of the opinions you can express online.
The other alternative is ISIS and alike doing recruiting without limitation.
I promised not to post again so I'm sorry.
There are other options. They can do the same as telephone networks, which is say anything you want, as long as it's not against DHS / military / Secret Service priorities, which are mostly codified in law (no running the mob, doing ISIS attacks, or capturing the Capitol by force). Just use that standard. That's fine.
Tech companies are having a fourth option, which is, let people post things that obey a corporation's TOS (designed to aid the corporation's profit maximization and virtue signaling), while *at the same time* also becoming people's primary means of communication *and* distributing news. Fully capturing most of the population's ideas and shaping them!
That's a very uncomfortable and conflicted set of priorities. No citizen or policymaker wanted this situation to happen. They knew corporate media was dangerous, giving rise to Equal Time doctrine, flawed as it was. Today's situation was weaseled into by greedy tech companies, who really don't care if they make society burn.