This is a problem with monopolies, not censorship. When private companies are forced to publish content, you have fundamentally lost the notion of a free press.
I don't entirely agree that companies operating public discussion forums is equivalent to "forced speech", but I do agree that the problem can be fixed by eliminating the monopoly/oligopoly.
Forbidding companies from moderating the content on their own public forums is forced speech. An easy test is when government officials participate in those forums: if you must publish what the government tells you to, that's literally forced speech.
Similarly, the Fairness Doctrine was overruled because requiring companies to air opinions they disagreed with was found to infringe free speech.
