Religious fanatics engaged in lunacy. Imagine that.
Whenever endogamous, highly structured groups reach a level of critical mass to the point that they almost never have to deal with outsiders, they begin to lose grasp with basic social norms.
This can apply to religious groups like the Old Order Amish, the Fundamentalist Latter Day Saints, the Satmar Hasidim, the Priestly Society of St. Pius V - but it can also apply to staunchly atheist organizations like the Socialist Workers Party USA, the NCLC, the Insititute for Objectivist Studies, Reichian organizations, etc.
This has more to do with narcissism than theism.