I think that the "fear factor" plays a big part in advancing fundamentalist worldviews. I also explain the very extremist, unbalanced views that a fundamentalist holds to some contributing factors of their personal upbringing. Most fundamentalist I've met tend to have been raised either very strict, religious or secular wise, or very liberal by their parents. This tends to create a very unbalanced, one way or no way, type of thinking amongst them The first type of upbringing I mention is a logical conclusion of an overly strict childhood dominated by domineering parents. In this persons mind, they need some type of rigid boundary system that cannot by arbitrated because that is the way they grew up and have come to understand life. Since they havenow become adults and are no longer subject to their parents discipline, another figure must replace the parent as the dominating factor in their lives. Since most fundies are of a religious nature, its no big suprise to find out what figure that they look to for guidelines in life. This becomes God (or in many cases, God as interpreted through their religious leaders).
The second type of person, one with a very liberal upbringing may come to feel a sort of revulsion to having had such an undisciplined childhood and seek a fundamentalist path in order to compensate for that lax upbringing. The sad thing is that most of these people are and never were really bad or wild as children (those that were often continue so throughout their lives feeling no guilt for not having boundaries as children. These latter type of fundies feel a great deal of repressed guilt and usually suffer from a mild to severe inferiority complex. They constantly see themselves as bad people who need some type of (usually every) guidelines and discipline to live by. This is really made worse by their exposure to fundamentalist religion which usually seeks to make everyone feel guilty about everything.
A fundamentalist often feels that there view is the only one because those views have become precisely that for them. They could not imagine living a life outside of the structured world which they have placed themselves in and certainly cannot imagine anyone else doing so. They therefore feel it is their duty to indoctrinate as many people as possible into their ideology so as to "share" with others that which has made them what they have become. A fundamentalist needs our prayers and support Often time fundamentalist groups operate In a very cult like level and anyone seeking to leave those groups will be subjected to some very real pressure not to, both external and internal. The latter, mental form of control is the worst. Remember that a fundamentalist has serious psycological issues dealing with their own sense of worth as well as a constant guilt compels that afflicts them. Since they also hold a very strict authoritarian view of God, it only follows that they believe this God will come after them in some way and try to cause harm to them in some manner. It may seem silly to you if you've never experienced this type of thinking but, believe me, it can become a nightmare to those who experience it.
A fundamentalist who tries to escape their rigid creed can go through some very hard times. Many may sadly become either atheist or agnostics because of their experiences. If you want to help a fundie get out of his worldview then show a lot of love towards them and try to explain That God is not a cruel tyrant who seeks to strike them down for very little infraction, but a loving father who they should turn to in faith and not out of fear.
PS. I also think that secularist can become just as much a danger to our society as religios exremist.