No, but I can certainly imagine a printing company refusing to print something they didn't like, or a TV/radio station refusing to air something it doesn't like

No, but I can certainly imagine a printing company refusing to print something they didn't like, or a TV/radio station refusing to air something it doesn't like. The post office doesn't have to mass-deliver pamphlets for you at less than the cost of posting a regular letter if it doesn't like them. One-to-one communication isn't the same as mass communication, and people have generally enjoyed a great deal of leeway when having private conversations vs mass media. Very little on Facebook is private - that's the point of it. The right to free speech, if literally nobody agrees with you enough to help distribute your media, protects nothing more than your right to stand in a busy city square with a megaphone. That has always been the case - it's not a new phenomenon with Facebook. Those with radical ideas have always been silenced, and still are on a regular basis.