A lot of people here have been trying to defend free speech as a human right, and a right that all people and corporations have a responsibility to preserve. No matter how many appeals to authority, appeals to history or long-winded explanations used all these arguments have fallen flat on people who either don't agree with free speech, or believe it's only the problem of a small number of institutions.
I believe there's enough people who support speech as a human right that these companies will end up on the wrong side of history and be superseded by more content-neutral hosts. It would be nice if this had more support, but there's enough people demanding companies, who are denying service to groups with the intention that they are unable to find hosting elsewhere, that I think the near future of speech is safe, and will come back stronger.
EDIT: Reworded second paragraph