I guess I don't understand how newspapers running ads against opinion pieces is any different from social networks running ads against posts. Also, that hasn't gone away? The Internet has changed how news publications work, but they definitely still exist!

But also, insofar as "town square" means that everyone can contribute, it's a better analogy for the Internet than it ever was for newspapers. There are no gatekeepers! Social media companies may have big megaphones, but they absolutely do not set the terms of acceptable discourse.

Like, what is it about the Internet that doesn't fit your description?