Eliezer's old post Every Cause Wants To Be A Cult is probably relevant here:
A Noble Cause doesn't need a deep hidden flaw for its adherents to form a cultish in-group. It is sufficient that the adherents be human. Everything else follows naturally, decay by default, like food spoiling in a refrigerator after the electricity goes off.
In the same sense that every thermal differential wants to equalize itself, and every computer program wants to become a collection of ad-hoc patches, every Cause wants to be a cult. It's a high-entropy state into which the system trends, an attractor in human psychology. It may have nothing to do with whether the Cause is truly Noble. You might think that a Good Cause would rub off its goodness on every aspect of the people associated with it - that the Cause's followers would also be less susceptible to status games, ingroup-outgroup bias, affective spirals, leader-gods. But believing one true idea won't switch off the halo effect. A noble cause won't make its adherents something other than human. There are plenty of bad ideas that can do plenty of damage - but that's not necessarily what's going on.
Every group of people with an unusual goal - good, bad, or silly - will trend toward the cult attractor unless they make a constant effort to resist it. You can keep your house cooler than the outdoors, but you have to run the air conditioner constantly, and as soon as you turn off the electricity - give up the fight against entropy - things will go back to "normal".
I think it's more that that every cause wants to be become a cult or a habit. The one thing causes don't want is to became reliable ways of achieving their stated goal.
Part of it is that people need social networks, but at least until the net, it was hard to make those networks happen just because people needed them. Either there had to be a cause, or the networks happened by geographical default.
When the goal of a organization is no longer feasible, the organization may look for another goal rather than dissolve. I'm not cynical about disease-fighting organizations which don't go away just because the disease has been abolished. It's simply too hard to build substantial organizations.
I suggest that there are default patterns for social groups, and they could be viewed as high entropy-- what you'd expect without knowing more than that there was a social group of a certain size, possibly with some modifications for tech level and status.
For example, I think that authoritarianism is the default for government-- "we're in charge because we're in charge, and it would be dangerous for anyone who tries to change that". Totalitarianism is lower entropy-- it's surprising for the people in charge to have an ideology which requires them to make drastic changes.
The recent Elitist Jerks: A Well-kept Garden describes an effort to fight one sort of entropy (the repetition of the same questions and answers) which resulted in another sort of entropy (an excessively stable and eventually fragile core group).
Maintaining fun is another challenge in the keeping things alive category. Pleasant is relatively easy. Fun (which I'd say requires novelty) is harder, and I'm interested in comments on what it takes to keep the fun going.
There's a theory that life exists as chaos on the border between order and randomness-- I find this plausible, and it's a different angle for looking at the Friendliness problem. How can a system be built which continues to permit (or even encourage) interesting sorts of change, without permitting change so drastic that we as we are now wouldn't recognize the outcome as still related to us?