Ok, time for a Civics lesson. Let's talk about what freedom of speech actually protects.
The government can not censor you, arrest you, penalize you, etc for what you say. Even within that, there are limits. You can't endanger the public or incite violence with your speech. You are protected from the government.
Now let's talk about what isn't protected. Basically everything else. What you say can have consequences. If you lie at work or speak badly of your company, your company can fire you. That is not protected. If you say something your buddy doesn't like, he can stop being friends with you. That's not protected. If you go onto a social media site and violate their TOS, they can ban you for 30 days. That is not protected.
I'm not defending FB. They are horrible and I don't personally like them. So I don't use them. That is my choice. That being said, they have every right to set any policy they damn well choose and you have no rights to free speech on their platform. None.
The inceicent whining about FB on private social media is ignorant. Don't like them? Don't use them. Encourage others to not use them. But you have no right to say whatever you want and be free from real world consequences. You never have.