No, but that would be Facebook exercising their freedom of speech. They would be exercising it badly, but they would be exercising it.

If you think that Facebook exercising their freedom of speech badly (in some people's opinion) is a freedom of speech problem and therefore they should stop it, then why isn't Milo exercising his freedom of speech badly (in some people's opinion) a freedom of speech problem and therefore he should stop it?

There are good arguments why Twitter should not do this. But they have nothing to do with freedom of speech.