How is silencing any speech a win for free speech? Don't you see that this could set a harmful precedent?

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?

One is a gigantic social media platform that millions are influenced by exercising censorship on public discourse. The other is a minority journalist's voice. Still think it's not an issue?

I agree with you that it's not a First Amendment issue, but it's still quite obviously a free speech issue, and it's sparked a much-needed debate over whether progressive-leaning social media giants should serve as impartial moderators of political discourse.