The issue is that, unless we have some sort of political movement toward a US-Government funded equivalent of YouTube, there will never be a public space online for the average person. More and more of daily social interaction is moving onto a platform on which everything is inherently private, where there is no public square anymore. I'm concerned about a future where technically you can scream on a physical public streetcorner but have it mean nothing at all in terms of impact on public discourse. "What good is speech if you are unable to make a phone call?" to twist the Matrix quote.
>If you want to publish your content with your own hardware on the Internet, you can. The tools aren't very good to do it, but you can. When the problem becomes network providers censoring your views, then come back to me.
The problem is that there's nothing fundamentally different about the arguments when it comes to the network providers. They're also private companies, why should they be forced at gunpoint to deliver content they disagree with? And yet we acknowledge that having the phone company shut you down for political speech on their phone lines would be an overstep even though the phone company is private.
At a certain point, the sheer dominance and size of some of these social media networks means we should be treating them differently. The fact that, as you say, "People treat Facebook, Google, etc. etc. etc. as if they themselves are The Internet" means that there is a distinction of kind that the citizenry are perceiving. I don't think the solution is just to say they're wrong, but rather to find a way to formalize this implicit categorization into something workable.
It seems like the options are to regulate, nationalize, or build government-funded public alternatives to mega-social-media systems. Other options are to add some better system of decentralization that nonetheless allows users to access the common public pool of an audience and not just ghetto-ize themselves into irrelevance and destitution.