One, Two, Three, Four Who's Punk/Geek, What's The Score?

This article on The Mary Sue discusses one of 2012's biggest pot stirring topics in the world of geekdom: the fake geek girl. I'll let the article speak for itself as the first 2/3 does a great job of introducing and analyzing the issue at hand. The part that really interests me comes after the line "Why does the impostor  who represents a small fraction of our community, seem to have grabbed so much focus and power?"

As a lifelong geek and a more recently self-identifying punk, I'm very familiar with the witch hunt mentality that develops around seeking out fakes and impostors in outcast social groups. The punk world particularly has dealt with the issue since the music first moved out of the basements and garages and onto the airwaves where anyone could hear it. Arguments over who or what punk really is still rage to this day. There are even punk songs about the topic such as Jawbreaker's "Boxcar", wherein Blake Schwarzenbach advocates dropping the labels completely because who cares?

The article covers pretty much all the bases in exploring why this behavior occurs. What really interests me though (and what I'd love to see someone with the appropriate background delve into) is the anthropological underpinnings of it all. What is it about outcast groups that seems to drive them to so vehemently weed out impostors and how far back in the human psyche does this reach?