That still doesn’t say that they have to allow completely free speech.Being held liable for content that's posted on their platform. ARRSE would be in trouble if you libelled someone on here but Twitter wouldn't if you did it on there. They have this under section 230 of the Communications Decency Act in the US as they are deemed as a platform if they dont exert any editorial control over the content (e.g deleting content which the owners don't agree with). If you want that protection you have to remain impartial, if you want to take a position you lose the protection and have to moderate accordingly.
A US piece of legislation does not apply in the UK. It doesn’t allow for comments in the US that breach the law in terms of racism, as an example. All it means that (in the US) they can’t be sued if someone libels someone or similar. There is no similar provision in UK law that I’ve seen. They’re still at liberty to allow or not allow content as they see fit as it’s a privately owned company.