The argument is that moderation should be done by publishing companies and who face liability for their content. It should not be done poorly, en-mass by platform companies who do it at scale using automation and don't face legal liability when they mess up.
The only exception I see to this is to allow community organized and run moderation for noncommercial communities.
They would - and and they are. That's why it's easier to publish fanfic on the internet than with an actual publisher. Tumblr is not on the hook for unauthorized titillating usage of copyrighted Disney characters, but HarperCollins would get sued to bankruptcy if they attempted the same. This is why the calls to repeal section 319 is idiotic - it will lead to more "censorship"
The argument is that, instead, these other, non-publishing, major communication platforms should be treated how we run other major communication platforms in the past, such as the telephone network.
We have existing laws, that could be extend to cover other communication platforms.
Telephone companies have been required to do certain things for decades, and the world hasn't collapsed because of it.
I'm not a libertarian by any means but I do have some amount of faith that if what you're describing comes to pass, the free market will provide alternatives, if demand exists. VPNs are one such alternative.
I truly believe that it's harmful to society to guarantee free reach to everyone. It's kind of like the paradox of tolerance, if you've heard of that -- if private entities are barred from moderating content on their systems, the discourse will devolve more than it already has into conspiracy, hate, and other forms of unwanted content.