This worked for a long time because much of the population of USENET had been socialized to take pleasure in generosity and respect the commons. With, of course, many, many exceptions. But there were enough posters who did get the basic idea that the system worked and largely policed itself.
This used to work because USENET was first populated by a hacker elite that took great glee in creating a culture of its own and had some familiarity with different ideas about how a society could work. We weren't all anarchists or socialists, but we had all heard of such things. You don't have to think such ideas are appropriate everywhere to think they are appropriate where the exchange of information is concerned.
It no longer works because the newcomers to USENET are not used to doing things on the basis of mutual aid, and because there are so many newcomers at once. USENET has always assimilated a new crop of newcomers every September or so, but this is another matter entirely.
There are three possible responses to this:
1. Ignore it and watch USENET decay. Complain about it a lot. Common variation: wash your hands of the whole mess and leave. I'm tired of this response.
2. The elitist approach: try to keep newcomers out. This doesn't work: eventually the larger group of newcomers will batter their way into each secret hideout, at which point we will flee to the next hilltop, and so on ad nauseum. I'm tired of this, too.
3. Take advantage of our technical knowledge to assimilate the public instead of the other way around! Set up automailers in every newsgroup we care about to contact all first-time posters. Send friendly, respectful, comprehensible welcome-o-grams, instead of obscure inside jokes. Be honest: openly embrace the principle that USENET is based on mutual aid. Find better metaphors in the experience of the average person to help explain this. Don't disdain the familiar.
Why do I think this can work? Because it used to. At one point, most new posters were contacted by at least one more experienced USENET poster (ie, a followup, an email, a flame, whatever). This has stopped happening because the newcomers vastly outnumber the experienced posters. But by setting up an automailer in each newsgroup, we can solve the problem of inferior numbers and make it practical to contact each newcomer once again. Of course, we have to write automailings that do not baffle, condemn or condescend.
I also think this can work because it is working right now in comp.infosystems.www.authoring.cgi. This group looks like the old USENET: there's not much dreck -- mostly content. (Actually, that's better than the old USENET!)
comp.infosystems.www.authoring.cgi is "self-moderated." That means that every poster has to "approve" his own first message, after reading an automatic reply that explains to them how to do that. In order to make this happen, an election was held, which is the usual procedure for switching a newsgroup to moderated status.
Self-moderation doesn't do away with willful ignorance or spamming or a thousand other ills. What it does do is give people a chance to better understand USENET, before their first posting appears. I hope that this will have a profound effect on the quality of discussion in the CGI newsgroup and in USENET as a whole.