The right to free speech is not the right to a receptive and interested audience. When Facebook or Twitter flags, deletes, or interjects their own editorial comment on your post, it is not an infringement of your freedom of speech. They are simply reminding you that you have voluntarily agreed to subject yourself to censorship in exchange for access to their user-friendly, free platform. You remain completely able to say whatever you wish elsewhere in a blog or on your own website, or for that matter, on the front stoop of your house.
You just know that you will have to work much harder to have your voice heard. By making it easier for you to have an audience, social media companies have tricked you into a kind of dependency. It feels unfair when someone pulls away your crutches, until you remember that you willingly sold them your legs.