Background info: a splinter group, which broke off from the LDS ("Mormon") church ~100 years ago, refusing to give up polygamy, has been in the headlines over the last year; their leader was sentenced to life in prison for rape of teenage girls he took as plural wives.

Deseret News, Sex banned until Warren Jeffs' prison walls crumble, FLDS relatives say

"As the year comes to an end and the followers of Warren Jeffs await the apocalypse he has predicted, they're living under a challenging edict: they're forbidden to have sex until Jeffs is sprung from a Texas prison.

It's one of the strangest edicts in a season full of them. Jeffs has issued a stream of revelations, prophecies and orders to his congregation in the border community of Hildale, Utah, and Colorado City, Ariz.

The recent edicts from Jeffs' prison cell seem to be having two contradictory effects. Many are leaving the FLDS faith in disgust. Those who stay are reported to be increasingly devoted to a man who is serving a lifetime sentence for raping underage girls.

According to numerous critics and outside observers, the imprisoned FLDS leader has sometimes acted through his brother Lyle and other times has spoken directly to his congregation over the phone from prison. He recently banned many of the things his followers enjoy: bicycles, ATVs, trampolines, even children's toys. But the sex edict reaches into the bedrooms of all his devoted followers.

According to Holm, Jeffs declared all existing marriages to be void....."they have all been told that they are not to live as husband and wife"....Holm thinks about 100 members have left in recent weeks from the community of 10,000.

Eliezer, Evaporative Cooling of Group Beliefs

Why would a group belief become stronger after encountering crushing counterevidence?

In Festinger's classic "When Prophecy Fails", one of the cult members walked out the door immediately after the flying saucer failed to land.  Who gets fed up and leaves first?  An average cult member?  Or a relatively more skeptical member, who previously might have been acting as a voice of moderation, a brake on the more fanatic members?

After the members with the highest kinetic energy escape, the remaining discussions will be between the extreme fanatics on one end and the slightly less extreme fanatics on the other end, with the group consensus somewhere in the "middle".

This doesn't simply seem to be a case of a new weighted average after some skeptics are gone (only 1% of FLDS have left). There are other dynamics going on among those remaining.

The image that comes to my mind is a lot of points scattered along a skepticism/fanaticism axis, and a repelling magnet placed on that line. This magnet pushes the already-skeptical values into greater skepticism (and out) and pushing the more fanatical members into greater fanaticism. How well does that actually represent what's going on? Not sure.