It's always odd to me when someone is talking about a public backlash and this is the response.

Did they say anything about legality? Facebook is free to do what it wants and the public is free to criticize it.

Legality isn't a magic shield against criticism.

>defend censorship of a website that doesn't have any illegal content

yes

Except they generally can't. See limits on who they can hire and what speech they can engage in. So we already limit the powers of companies to protect the rights of people even though we could have just told the people work/shop/go somewhere else. Why doesn't that logic also extend to speech?

Sure, and we as citizens can hold these private companies accountable by voicing our concerns to our government representatives who can enact legislation to prevent companies from doing whatever they want.

and they as a billion dollar company can voice their concerns to lobbyist who will then convince the government to do nothing