All valid points but it would only be a free speech issue if Facebook was a government or publicly-supported institution. Mosques have the right to block Christians from proselytizing on their premises (and vice versa). That's not preventing free speech (they're still totally free to stand on a streetcorner and vent), it's giving the guy who owns the private property the right to use it the way he wants.
People often misinterpret free speech as meaning they get some kind of universal pass but free speech actually has very specific limits (and for good reason).