Free speech is only an unalienable right, in the US, from the government. Not facebook, not google, and certainly not individuals suing a private entity.
Everything else stems from the public and historical landmark court cases related to free speech- and the benches of the supreme court have staunchly defended freedom of speech from the government.
You’re confusing the concept of Free Speech and the law codified in the First Amendment rights. Free Speech as a concept is (by necessity) much broader (both as defined in the declaration of human rights, and as envisaged by the thinkers who originally proposed it). It doesn’t mean “there’s no accountability whatsoever” but it does mean that there’s an active duty to uphold individuals’ rights to articulate themselves. Unfortunately this confusion is extremely common — even the Wikipedia article restricts it to government intervention in the opening paragraph (but then broadens it).
And that debate is ongoing; for example, you can be held accountable by the government in certain cases (see "Seven dirty words").