[Ol' Dan Tucker]

Here they violate the First Amendment in the most basic terms.

1st Amendment only says that the government may not restrict free speech.

It says nothing about a private party restricting free speech because that's none of the government's business.

[SmokingJoe]

While the First Amendment generally does not apply to private companies, the Supreme Court has held it “does not disable the government from taking steps to ensure that private interests not restrict . . . the free flow of information and ideas.”
That would apply directly to Twitter Facebook Google YouTube.

[Crucial]

And yet it is the government that eliminates the recourse of the injured or silenced party.