I just read an interesting article by John Dvorak at pcmag.com about social networking and how fickle the users are. He speaks of a betrayal on a past network that caused a rift and the eventual downfall of the group. He also reminds us that these social networks are not real communities but imaginary with the illusion of reality.
While I can see his point I also have seen that this type of behavior is seen in the more tangible social groups. I have seen small church groups that are being lead down a path by a skilled social engineer, bleeding them dry of funds. We have seen political groups turn on their leaders because of some real or perceived failing, the Clinton/Lewinski issue and the Watergate/Nixon issue. The followers of each person took up sides and shook rakes and pitchforks at the other for turning.
I am not convinced that our virtual social networks are any different from physical networks other than they span great physical and demographic divides. People move on to new politicians, new churches and new football teams just as they move from myspace to facebook and the next big thing. I think it is just human nature to take up a position about some person, topic, issue, war, or product and defend that position.