The rigidity of one's religious beliefs diminishes with the presence of faith. Fanatacism is a grasping for order in a mind without peace and without faith.
Fundamentalist is a person who considers whether a fact is acceptable to their faith before they explore it. As opposed to a curious person who explores first and then considers whether or not they want to accept the ramifications.
Some people live closely guarded lives, fearful of encountering someone or something that might shatter their insecure spiritual foundation. This attitude, however, is not the fault of religion but of their own limited understanding. True Dharma leads in exactly the opposite direction. It enables one to integrate all the many diverse experiences of life into a meaningful and coherent whole, thereby banishing fear and insecurity completely.