If you have to resort to that degree of hyperbole to make the problem seem problematic, it only suggests that it isn't much of a problem in practical reality.
The deliberately hyperbolic scenario which results from what's being proposed here - that platforms be forced to publish all legal content regardless of their intent - is that governments declare all websites to be platforms, and thus governments directly control all online communication and publishing, and then simply declare any speech they dislike to be illegal.
In essence, what is being argued is that in order to protect free speech we cannot trust private citizens or any communities they form to exercise freedom of association. Yet the same community that considers everything else that governments do a violation of their fundamental civil liberties and a naked and obvious pretext towards rounding up dissidents for the gulags seems to implicitly trust the same governments to act as fair and impartial arbiters of online speech, to the point that they consider giving up what were (until some point in 2016) considered essential liberties to be a necessity.
If the scenario where governments cede all of their authority and property to private interests you mentioned earlier is reasonable enough to be actionable, then this scenario which at least describes things that governments have historically actually done, should be even more actionable.
Yet, given the choice of Facebook not having secret police, and it being possible to simply create other networks on the open internet if you disagree with Facebook's terms, and Facebook having secret police, and the creation or moderation of any new network being directly overseen by governments, and terms of service being enforced by the state's monopoly on violence, people would rather Facebook have secret police.