This has become such a common trope that I think people fail to apply even a modicum of scrutiny: the internet is not the town square and whatever your idea of the town square is likely wrong if you think its as wild-west-y as the internet is.

Firstly, try to approach children in the town square while wearing a mask for anonymity; or try to hold up images of porn in your town square. You will not be there long, you'd likely be detained, and you'd likely be asked for identification.

Secondly, why do people think there is some sort of town square? I have lived in several large US cities and several small towns. In neither was there any sort of common place where we all congregated to address matters of the town. At best, there are city hall/city council meetings where the public can speak but at least in my town (and I know of many others), identification is required to prove that you live in the town!

Even the founding fathers, when writing under pseudonyms, understood that anonymity and circulation was incumbent upon them to maintain, not that they were entitled to it because "town square."

To address your last point: this is not simply some ill conceived moral panic/think of the children type moment. Go try to host - as an adult - an AA meeting or "computer meetup" with children that happens to be held in the local adult toy shop. See how well that goes for you. At this point, we know children are getting approached by adults at a large scale on instagram, we know children are getting exposed to a lot of adult content on twitter, and on the spectrum between innocent HOA meeting and damaging to society as a whole, its clearly more towards the latter.