And arguably, even at small scale, town squares don't lead to decency or better decision making. Things that "sound good" are judged as correct without research, data collection or analysis, with the predictable results.
Town squares sound great, but every city square I've been in is full of yelling and pickpockets.
"Healthy" doesn't seem like the word to use to describe something that requires constant and intentional intervention/manipulation by some external party merely to exist.
At least some relatively high degree of inherent self-sufficiency, resilience, and robustness should be present for something to be considered "healthy".
“Healthy” is not some absolute end state, but an ongoing process and a destination that is never reached permanently. Physical health is a useful analogy here: attaining it is the result of constant and intentional intervention. Ceasing to intervene results in an automatic trend towards unhealthy.
> some relatively high degree of inherent self-sufficiency, resilience, and robustness should be present
The existence of these properties in humans does not automatically lead to healthy outcomes. The entire self help industry exists on the basis of our struggles with using these properties to our advantage.
When you look at social media as a manifestation of human thought and behavior, I think a similar conclusion can be drawn: healthy communities will only emerge where deliberate actions are taken on an ongoing basis to maintain health. The existence of tools and inherent properties to enable this endeavor are necessary but not sufficient in and of themselves. Humans are always the complicating factor.
The healthiest imaginable individual has an immune system constantly fighting off infectious agents. Their liver and kidneys are filtering toxins that their own bodies are generating. You're healthy if all your defense and maintenance mechanisms are constantly doing their job. Health is an ongoing process.
The internet doesn't allow this, you are talking with what a hundred posters in a single thread sometimes? Going across multiple threads it will be thousands of not tens of thousands even if you tend to focus on niche threads.
Thus somebody needs to filter.
And before somebody brings up OPs broken "if everybody talks we will be fine" argument the simple reality is that isn't true.
The reason is filtering doesn't just happen on a person to person level. Much more importantly it happens on a site level.
If people find what they are discussing isn't valuable they will leave the site.
Once a group forms of those who want to cause chaos they will push away normal users.
Thus your choices are choosing who you leave on your platform blocking those who would push away your user base, segregating your user base (ideally in a way that allows some cross pollination) to allow the chaos to be isolated from most users, or becomes just pure chaos ala 4chan.
Note I am not saying you can't have good discussion without moderation. Certainly you can. It just isn't what the majority of content becomes.
After all low effort content is low effort.