The first time I "met" people who weren't involved in tech online was probably Friends Reunited (school friends) and then Facebook. Reddit, Twitter, Instagram, Snapchat and TikTok are all far more diverse than Usenet ever was (although I only ever use Twitter these days, so that might have changed).
I therefore can't accept your view that it had a dramatically diverse group of participants. It has an even less diverse group of users today, and it's worth remembering we should probably not talk about it exclusively in the past tense: it's still an active thing.
On the authority thing: the OP link suggests a public shared space has to be owned collectively, and therefore the policing model that Usenet lacked (other than a few good actors at the edge of the network like you suggest), will eventually be its downfall. We see this in unmoderated spaces all over the Internet today.
All public spaces are at risk of anarchy without some sort of policing, once populations reach a certain size. This is not a uniquely digital/online phenomenon.
I wonder if it's possible to create a protocol where policing is built in somehow, whilst retaining the public commons features that the OP desires.
I recognize you from afu! I only lurked, but I inevitably think of that group when I remember how good usenet used to be.
I don't think it's exactly a matter of authority. A university wouldn't care about someone merely being a troll in Usenet; they'd have to be breaking a law or otherwise acting egregiously to attract disciplinary action.
Instead, I think it's a matter of reputation. A smaller community is one where everyone is likely to be familiar with everyone else on an individual basis, and a community with a technical barrier to access imposes a transition cost on someone wanting to take their ball and go elsewhere.
In my opinion, both of these things act together to change one's target audience and engagement style. In such small Usenet-style communities, a user is speaking to that community at large. In larger forums with less individual reputation and lower barriers to access, the forum instead becomes more of a performance place: people are speaking to a subset of like-minded supporters.
Twitter is a great example of a very large forum with a near zero-barrier, where I can shout at an adversary while speaking to like-minded people.
How so? It was universities, tech people in corporations and a few folks that just had PCs as a hobby. In short: upper middle class (because those things are expensive), educated (because it really wasn't as simple as it is today) and with time on their hands.
There may been some diversity in political leanings, but on the fundamentals, education, social class etc?
(The only exception is if by "diversity" you mean "exact proportionality of representation"... but that's not the same thing. If you want to say that, go ahead. At that point I will agree with you that there wasn't exact proportionality of representation... but then, there isn't today either, nor is it even clear how one would get there, especially as you crank the requisite "exactness" up. Two decimal places? Four?)
My point is that it's a diversity of opinions (maybe; they tend to be closer together on the important things, too, demographics predict politics fairly well after all) and of hobbies or interests, but not of backgrounds, i.e. where the rubber meets the road. I understand that people usually do not mean "the conservative child of lawyer A and the progressive child of investment banker B chat about their shared interests with the apolitical child of entrepreneur C", but "the child of a lawyer, the child of an office worker chat with the child of a day laborer".
Again, I don't mind it not being or having been like that, I don't see any intrinsic value in diversity by itself. Calling it diverse just sounds like a misrepresentation of what it was.
A single university is an wide spectrum of participants. Yes, there are some demographic commonalities, but there are so many significant differences. Now add universities across the spectrum and across the globe.
Is it? Sure, you'll have people studying physics, law and economics, but they'll be pretty similar in background. I'm not saying that usenet was a hive mind, far from it, but it certainly wasn't very "diverse" with regards to the background of participants.
Who knew this was debatable. Every race, creed, religion, and demographic (even if skewed slightly to the higher end). Every political lean imaginable. People in sports programs, arts programs, and every other nature.
The notion that this group has some natural agreement is not reality based.
It started to fall apart when the nodes on the network included every ISP, etc. When people who have no authority over the participants, and no real punitive avenue if they broke conventions, it started to fall apart. Even if you got banned from that node, there were thousands of other nodes to jump to and continue your abuse.
[1] When you went to some university, the account they provided you was your authentication on Usenet. You had that single account and it was your sole key to the network.