In any religion. What causes a person to take their religious book the most literally one can possibly take it? What causes a person to demean and rail people who aren't their religion? What makes people feel they should shove their beliefs on others? In other words- why do people become fundamentalist? Is it insecurity issues? I just don't know. Why would somebody want to take the extreme position?
Humans have in their nature, everything that exists in the nature of our world. Part aggressive and part passive. Some people are more aggressive and some are more passive, just like animals, but harboring more complex qualities, like ego, insecurity and lust for power among others. I think it is mainly those three things that make up fundamentalism though. Take a person with an aggressive nature who is insecure with themselves, hungry for power, and who has an already overblown ego... now put religion in their hands, and they will wield it like a shotgun.
To embellish on each quality...
Ego: The prince and princess syndrome of little children, nurtured into adulthood until it creates a monstrous sense of self-importance and self-rightousness. Loving yourself, and thinking you are better than everyone else are two completely different creatures. The problem, when you think you are better than everyone else, is that it is a constant struggle to prove this to yourself and everyone else. Everything is a dick measuring contest. What better way to satisfy this addiction for a sense of self-importance than to use "divine intervention," a holy book, and a whole religious organization?
Insecurity: I think this explains a lot about people's actions. Insecurity I think is the root of jealousy. If you love yourself and are confident in yourself there is no need to be concerned with others. Period. Improve don't envy. People feel insecure about their origin, their nature, and their death. Religions provides comfort and control here. Many people including fundamentals find happiness and comfort here, and they want to help others find it as well so they justify extreme measures. Humans have a dual nature of opposites, and our social contract keeps most of the dark elements of our duality in check, bust most are conditioned to think in an extreme way in that the dark part of our duality should be totally eliminated instead of loved. People are insecure when they are entertained by sexual things, violence, or other "bad" things, and instead of working with it, they take the religious idea to eliminate it, and instead make it worse a lot of the time, becoming more fervent in their desire to eliminate as their own problem becomes more serious. I think in psychology this problem is a psychological defense mechanism called projection. Lastly, people fear death. Then there are those like me who don't necessarily fear death, but fear being without those they love. The answers to this problem that religion provides is a control mechanism that works through comfort and fear. Without the insecurities, there would be no need for comfort and no place to instill fear. This both draws the insecure to the fundamental religions, and then builds them up into a blind sense of security, which is then projected on outsiders.
Lust for power: Religions have so many control mechanisms to put at the hands of people with this complex it is ridiculous. Original sin, the atonement, control of sexuality, submissive rituals and practices, etc. People who want power and don't have the means to get it any other way have no further to look beyond having a say so in someones salvation.
If you want to understand why a religious group acts the way they do, take a peak at their god or gods. They usually mirror each other in many ways. In the case of fundies, you will see that just as they are in denial of their personality and character flaws, so is their god.
Or maybe they were raised that way and most people don't really like change.
