This is a real philosophical problem that must be dealt with. What are the rights of private platform owners when their platform carries a significant proportion of citizen communication and information sharing? Note this problem is entirely a consequence of centralization
Collusion between the members of the oligopoly is the problem. Additionally, they take advantage of the marketplace by creating ecosystems and wield that power like a monopoly. If one decides to ban someone, ok. But all 4 at the same time blacklisting people? Not acceptable.