I submit that what, or rather who, kept comp.lang.lisp alive for so long beyond most of the rest of usenet was a guy named Eric Naggum. He may not have identified the sociopath aspect, but did have the entitled MOPs in his crosshairs and kept them out with (sometimes utterly brilliant, btw) flamage.
Sadly, comp.lang.lisp also points to something not mentioned in the linked post: Entitled MOPs and sociopaths will not just silently accept their exclusion.
When excluded, they attack, possibly indirectly through other venues. To this day, in an astonishing number of online discussions of Lisp culture, you're apt to find attacks on comp.lang.lisp in general, or Erik Naggum in particular, for the high crime of having once excluded (for example) an entitled MOP who wanted his homework done by comp.lang.lisp.
Also, making things cultural versus rules is more effective, as the collective will help enforce a given way of things, to some extent.
Also, money. People who pay money are more invested and less likely to dick around. They paid money to be there, and will be more obedient of the rules and will enforce the same on others. But money is tricky of course, and can blow up in your face.
This article fails to understand that all groups have a life cycle. Clay Shirky's essay is the canonical explanation:
http://www.shirky.com/writings/herecomeseverybody/group_enem...
Nostalgia in online discussion groups suffers the same problem: you can't go home again, because you're not your previous self any more. http://davidgerard.co.uk/notes/2014/06/03/internet-fundament...