If they're really being collusive, then you investigate them for violations of antitrust law or otherwise figure out what they're doing that's breaking the free

If they're really being collusive, then you investigate them for violations of antitrust law or otherwise figure out what they're doing that's breaking the free market, and you fix it. Alternatively, if every company in a free market seems to believe that X is objectionable, then X is considered objectionable by all of society, and it's not the place of the government to override that. If Facebook bans 419 scams, and Twitter bans 419 scams, and Reddit bans 419 scams, and Craigslist bans 419 scams, a fake Nigerian prince shouldn't be able to lobby Congress for a Constitutional right to force these private companies to host his content. They're allowed to be "collusive" in establishing shared, society-wide norms - that's how society works. (Or we could conclude that we cannot make the free market so fair as to fairly represent all of society, but as far as the Overton window in the US is concerned, that's an absurdum, and so one of our propositions must be wrong.)