After years of thinking about online community ( not only the ones from America, but also domestic online communities here in China).
I noticed one phenomenon: the form "online community" seems to grow and develop very well in the English world like US. ( on the top of my head, stackoverflow, cgsociety, quora etc.). Posts on these websites have great quality, and people are willing to share sincerely, a great deal of discussions produced useful results, people participated all got inspired.
While, in China for example. Online communities doesn't pan out that well. News media theses days is filled with E-commerce, SNS and such areas that are much closer to the chain of wealth, no one really succeeded in building a high quality online society that really contributes back to really world, probably due to the lack of connection between deep meaning content and monetization in general ( except for those content that are closely related to money, like stock market analysis, startups\venture capital news, etc. )
I do realise that online world is based on real world, and we can not separately talk about them. So this difference in online community probably implies the mindset and social structure of the society it is based on.
Probably, the US has long gone past the phase that everyone worries about basic needs and survival. Americans already started to enjoy life on spiritual level, therefore they treats online world as seriously as real world, which led to responsible online activities( for one thing, they use real name online far more than Chinese ), which is the fundamental requirement for high quality community.
Speaking of atmosphere between online communities of east and west, members hold a higher tolerance bar in the west than here in China on content and information. It is seen everywhere that under Chinese authors' blogs, comments are filled with complaint and sarcasm, whereas not so much the case among the wider internet world where the same content faces responses far different.
Although, there is indeed no large high content quality communities in China, some narrow-focused communities still offers great environment for people who cares about high quality content. I assume, in a materialised and faith-less society, or probably every kind of society, in order to achieve extraordinary and exceptional, the size of crowd that can be gathered and works well is not going to be a big one. Like Clay Shirky said in his essay "A Group Is Its Own Worst Enemy
you have to find a way to spare the group from scale. Scale alone kills conversations, because conversations require dense two-way conversations. In conversational contexts, Metcalfe's law is a drag. The fact that the amount of two-way connections you have to support goes up with the square of the users means that the density of conversation falls off very fast as the system scales even a little bit. You have to have some way to let users hang onto the less is more pattern, in order to keep associated with one another.
Ultimately, there would exist tens of thousands of small communities, each has their own things to care about, in the same time, groups can form large groups together on some certain agreements, maybe a "tree" of human community would be the optimal form, I don't know.