Your platform may be legally allowed to censor everything, but it's clear it doesn't take freedom of expression seriously.
If we add some more mental gymnastics, we can say the Chinese government supports all legal freedom of speech as well. If this sounds ridiculous but the former does not, we should evaluate why one type of censorship means freedom but another means oppression.
A private platform is free to censor users as they see fit, as the users are free to A) not use their platform at all, B) use a competing platform, or C) create a competing platform. You are not compelled to post your thoughts on FB, or Hackernews, or anywhere else, nor are you entitled to a platform to do so there.
The flip-side, censorship by gov't, is platform independent. This is where the 1st amendment protects come into play, defending you (and the hosting platform) from gov't suppression regarding political or religious speech. If the USA hosted an official message board, then we could argue comparisons to China.