China bans content through government policy, and government policy carries the force of government which applies to all public and private parties. The force of government means laws, courts, police, and prison, which is typically the sole prerogative of government.

HN, BMJ and Facebook pay for their expenses as private parties and may not wish use their money to help you broadcast your speech. The main difference between HN and Facebook is that Facebook is Very Big.

If your idea of free speech means that either HN or Facebook must pay for a metaphorical Dang and other fancy engineers to maintain your free speech...