[martinpw]

Not quite what you are asking, but related, is the idea of evaporative cooling of beliefs, a selection effect where over time the more objective and rational holders of a belief are persuaded by the evidence that their belief is incorrect, and those who continue to cling to the belief become a progressively smaller group who are increasingly uninterested in rational argument or scientific evidence. This results in the group arguments becoming progressively more shrill and incoherent.

http://lesswrong.com/lw/lr/evaporative_cooling_of_group_beli...

[okreallywtf]

Interesting, maybe not the same effect but maybe one that works in concert.