Free speech is the principle that you should let people say whatever they want without censorship or legal consequences (excluding cases where the speech causes direct harm).

> They can do what they want with their platform.

Of course they can, but they can't then say they believe in free speech. Similarly to "you don't make peace with your friends" : you can't say you're free speech if you only allow information you agree with.

What annoys me is when people think that free speech isn't a principle, but just a law in the US which applies to the government only. It's usually: "Hurr duur, it's a private company so it can practice full communism and we should be okay with that."

(That said, personally I have mixed feelings about this because I feel like it might be causing harm... Same with the antivaxxer crap.)