This has been hashed out many times. Government cannot be allowed to use private companies as a shield. For instance (this has been tried in the US/canada/uk etc) can a city violate the rights of citizens if it hires a "private" company to conduct policing? Can a city ban certain people from walking the streets if it puts those streets in the hands of a "private" holding company?

So what if the government partners with all the large tech companies to have them voluntarily enforce restrictions on speech? Oh, you're free to say whatever you want, just not online. Or on the airwaves. Or in public parks, which were recently put in control of a private management company too. You are free to stand in your bedroom and talk to the wall. Just don't talk loud enough that your corporate landlord kicks you out for a noise violation.