Why shouldn't platforms be stripped of their legal protections (and some effectively destroyed) if they are exercising editorial discretion? Why shouldn't YouTube be responsible for the videos that they do allow/have approved?
If someone doesn't think that YouTube should be accountable for content, then should a newspaper be accountable? Should a person be accountable for his content?
In fact the only defence platforms like YouTube had was the telephone company defence you’re making (as it happens telephone companies haven’t been immune from the demands of censorship either) but the moment platforms do start self-censoring they lose that ISP/telephone defence because they’ve proven they can moderate contributions (even if that moderation is effectively worthless in a great many cases)
In many regards I think "common carrier" status applies. Private companies like ISP's, telcos, and parcel delivery services are not allowed to discriminate based on the content nor the individual. This is similar in spirit to "net neutrality".
The larger a platform becomes, and the more essential it is for communication and daily business, then the more important it is that it does not discriminate.
The grey area is that platforms like YouTube both are public communication platforms, but they also curate content as well. Not sure the correct answer in that case.
What muddies the water even further is that some platforms even pay contributors, albeit for ad impressions rather than directly, but again it makes the distinction more subjective than it appears at first glance.
Eventually there will come a point where the people outside the tech community will deem the responsibility of moderation greater than the the need for an open platform. I’m not sure which side of the fence I sit on but I do agree that the government mandating moderation has the dangerous side effect of raising the barrier for entry too high for any new players to challenge existing networks.
If the press have the editorial freedom to chose which of their reporters articles they publish -- be it factual, opinion, or even outright biased -- then why shouldn't other private platforms have the same editorial freedom?
The "who" in your "who gets to judge?" then becomes a simple answer: the platform owners. The uncomfortable part is that some platforms have a larger impression on people than others. But short of government intervention -- which is a hugely unpopular option in America -- that's just the markets working the way you guys want your markets to work (ie given the psychology of confirmation bias, if platforms were to focus on unpopular view points their viewership would diminish).
That's the paradoxical part of all this. The same freedoms are being used in both cases but in one instance it enforces principles you believe in and in the other instance it erodes those principles. But you cannot have one instance without having both.