When I was about eleven, Barbara, a girl in my class, invited me to hang out with her. I thought she was not very bright, but she seemed pleasant enough, so one Saturday I went to her neightborhood to hang out. I thought we would rollerskate or something. Instead she took me to a friend's house. There were a bunch of kids there who went to public school, so I didn't know them - Barbara and I went to Catholic school.
So we all hung out. I vaguely remember thinking that like Barbara, they were not very bright. We played on a swing set and talked. I don't remember the conversation, except the end, when Barbara informed me that her friends had decided they didn't want me to be part of their group. So I went back to Barbara's house and read her brother's comic books until my Dad came to pick me up.
Being kept out of the group wasn't a problem - I never had any desire to be part of their group, since I thought they were dullards. Plus I really enjoyed those comic books. But it was maddening that they seemed to take great pleasure in joining together to pass judgement on me.
Welcome to the Country Club mentality. I should know the anthropological term for this behavior, but Country Club mentality is a good enough description for the pleasure that most humans get in being insiders, both for the comraderie of other insiders, but also, and possibly even more significantly, scorning outsiders.
I've run up into this behavior several places on the Internet, most recently on Wikipedia. And I've noticed an interesting phenomenon. It seems to me that the Country Club mentality usually kicks when I feel like I'm starting to win a debate with an alpha insider. At this point the alpha insider will stop responding to rational arguments and simply pull rank, saying something to the effect of "I'm a member of this insider group so I know better than you, so that's the end of the discussion." Then the beta insiders will chime in to the effect of "yeah! You're not an insider. Acknowledge our superiority or we will shout you down." Sometimes they don't threaten to shout you down, they just shout you down.
Of course my perspective is not objective here. If I had time I'd look for a relevant anthropological study. And BTW - anthropologists are just as bad as any other group in displaying the country club mentality.