Fundamentalism speaks to the basic insecurity of the human condition.
We all live with this insecurity, but most people manage to adapt, and weave it seamlessly into their lives.
Others spend their lives constantly masking and propping up their insecurity, by latching onto something of a 'cause' that comforts them.
It's a 'gang' mentality - it's 'us against the world', it's 'we believe in this, and we are right, so we are a select group of correct people and the rest of the world is wrong.
Some fundamentalists affirm themselves by faintly pitying others, and spending time telling others who think otherwise that that are simply missing the point, and are lesser people for it - fundamentalist Christians do this.
Other fundamentalists affirm themselves by seeking to destroy others who think otherwise, seeing them as unfit to occupy the same piece of earth - fundamentalist Muslims do that.
But the root cause is exactly the same, a deep-seated fear of abandonment, and not 'belonging'.
As I said, it is part of the human condition - a need to feel a bond with others, and in extreme cases, to believe in utter self-righteousness.
It's easy to live with one set, harder to live with the other -
I was always able to ignore and laugh at Mary Whitehouse and her belief that only she and her select band of cohorts were immune to the tide of filth sweeping the nation via its televisions.
I can't ignore and laugh at the daughter of a terrorist who advises that innocent people must pay with their lives for the death of her father.
But the root human condition is identical - we either learn to accept and adapt, or we wander into the extremes of thinking in our deep-seated desire to be connected to others.