Freedom of speech and freedom of expression mean that the government can't put you in prison or punish you for saying or believing what you do. Facebook aren't the government, they're a private entity and don't have to host anything they don't like- including hosting photos that they don't like. It's a walled garden, and it's their walled garden, and if you don't like it you're welcome to leave.
And on the other hand: it's the only garden. If your friends are in that garden, they can't share with you, interact with you, etc, without you also being inside. Facebook's created a 'with us or not with us' distinction that has a very sharp boundary. And it's worked- they've won the social network wars. A billion people are on it.
The question is, as the social network champions does Facebook have to have to public's interests in mind or just their own bottom line profit margin? As a public company, the shareholders will fire their leadership if they don't choose the bottom line. As the major social network of the world, the public will denounce them for actions like this.