Well I've always thought that religion is like a software virus that corrupts thought processes.
Religion plants ideas and overrides or hijacks natural thought patterns.
Since God is given the status of the ultimate authority, followers are obliged to follow the leader without question.
Any rational thoughts and vague innate signals of empathy, say for first-borns, homosexuals, the unclean, hunchbacks, dwarfs, men with injured testes, or people born into the wrong tribes is crowded out by repetitive religious dogma and the fear of punishment for thinking otherwise.
If religious fundamentalism is to be recognised as a mental illness, then for the treatment to be effective it will have to go beyond the individual. It will have to be group therapy.
Here is a recent study that found religious extremists are motivated more by family and friends than information they found on their own i.e. on the internet:
Friends, family key motivators for extremist behaviour, study findshttp://www.abc.net.au/news/2013-08-08/motivations-for-terrorist-radicalisation/4874082
There is a strong group thing going on - and also why I'm so suspicious of religious spokespersons claiming that extremists don't represent the majority.
I think they fear reprisals but quietly rejoice in the madness. I suspect even the meekest Muslims are lifted by the radical terrorist acts of Islamists. And good Christians get a little thrill every time a drone takes out a Jihadist.
Fundamentalism is the tip of the iceberg - it can't float to the top without the quiet support of the silent sick mass beneath.