Generally, however, purity movements either abandon their quest for purity in favor of rewarding in-group status (see the treatment of recent Republican infidelity revelations) or they splinter into tinier sects, some still obsessed with purity, others offering various loopholes (see the Mormon polygamist groups).
None of these outcomes are anything I want to see for any group I'm involved with, so I twitch when I see someone trying to draw, for example, simple lines between what is and what is not feminism. And when I say twitch, I mean I tell y'all about it.
Most recently, I've been twitching about these big, overlapping groups of rationalists and critical thinkers who are out here fighting the good fight against various forms of irrationality.
It's hand in the blender time, I'm afraid. Over at Quiche Moraine.