One of the more recent agitations in one of my longstanding social circles brought me to the following conclusions:
Once formed, a community is self-governing in the respect that by participating in the community, and from the feedback of other community members, each initiate learns the community's expectations of its members and the acceptable range of behaviors within that community. (This can range from attending all of a religious congregation's services or a fraternal society's meetings to the expectation that subscribers to an e-mail list or social community will not "troll" or use abusive language in that venue, to membership dues requirements, titheing, and fund-raising.) Any person who is willing and able to meet that community's expectations may join the community. In return, each new member is also given a greater or lesser voice in changing those expectations as the community evolves.
There are a number of unstated expectations and behaviors that occur both within the community proper, and in that community's relationship to "the outside world". Some of these behaviors are purely social, such as the rise and fall of "alpha members" -- people whose initiatives and opinions are respected, or given more weight, regardless of whether or not they hold official positions of responsibility within the community. Others -- such as an unstated expectation of participation in events, or donation of operating or charitable funds -- may suggest that the community's goals may have shifted from its original purpose, but that its foundational documents (if any) have not been updated to reflect that shift.
It is often the unspecified, the underspecified, and the obsolete which create friction. In the interest of maintaining the community, it is the responsibility of the community and its leaders to periodically review its core documents, mission, and goals, and to update them to reflect the current goals and expectations of the community. Failing this, there will be friction between newcomers and veterans, and between factions within the community. If the community is unable to find some common ground among its various factions, either the factions will splinter off, or the community will collapse.
However, as long as there is a common interest -- even if that interest is limited to the well-being of the other members of that community -- a community will remain relatively intact, regardless of whether or not a formal structure exists to manage it. Its members will individually volunteer their time, goods, services -- and sometimes even money -- towards the well-being of any or all of its members and towards maintaining communications with that community. People one meets impersonally through the community become colleagues, friends, surrogate family -- and sometimes even real family.
It is that common interest -- the friendships with, and concerns for the well-being of, other members in our social community -- that has allowed it to survive scandal, friction, and factionization, for over thirty years.
It is that same common interest -- friendships, concern for each other's well-being, and the willingness to help each other -- that make communities out of our online social networks, and that will allow them to survive the tests of time.