Fanaticism comes from any form of chosen blindness accompanying the pursuit of a single dogma.
There are many different rivers that lead into despair: there's poverty; there's political repression; there's gender apartheid - there's a sense of culture loss; there's religious fanaticism.
The mistake we make is to attribute to religions the errors and fanaticism of human beings.
Time and again we see leaders and members of religions incite aggression, fanaticism, hate, and xenophobia - even inspire and legitimate violent and bloody conflicts.
From fanaticism to barbarism is only one step.
I don't think the 9/11 attacks taught us anything we didn't already know about religion. It has long been obvious - even to the deeply religious - that religious fanaticism is an extremely dangerous deranger of otherwise sane and goodhearted people.
This fanaticism is what feeds terrorism. And this is precisely why Muslims must play an active role in opposing hate sermons and incitement to terrorism and extremism in their mosques.
The interval between the decay of the old and the formation and establishment of the new constitutes a period of transition which must always necessarily be one of uncertainty, confusion, error, and wild and fierce fanaticism.
The tendency to claim God as an ally for our partisan value and ends is the source of all religious fanaticism.
But as in all cults, what's central to the Communist Party is the belief system and the elimination of nuance. From there you're very slowly led down the road to fanaticism and mass murder.