Fundamentalist is just a self serving descriptive term for something else entirely. Authoritarianist is the real name for the thing you are seeking to name. Everyone who believes in their faith believes that their understanding of that faith is fundamental. No one worships according to a doctrine they themselves believe to be false.
The problem is that judgment is granted over the very heart and soul of the membership of a sect. God gets set aside, oh so reverently, of course. The authority figure is given the place of spiritual guide, leader, and judge. Usually the authority figure must have some real world justifier for his assumption of authority, or at least at first he must. Theological scholarship is a frequent justifier. This is true in Christian, and Islamic fundamentalism. The public confession of faith is that the Bible or Koran is the true authority. The reality is that a huge plurality of believers are not intellectually prepared for or capable of the pure scholarship needed to interpret the meaning of scripture, and its application to day to day living in the twenty-first century.
The pragmatic human reason for this is fear, and sloth. We are all lost in this world. Most of us find it daunting. Making decisions is hard work, and learning even harder. The glib and educated have great power. Often they use it for great good. But the lure of power is deadly, and in almost every case religious leaders fall prey to its poison. The opinion of the leader is perceived by the follower as the opinion of God. This is true even if the leader himself is honestly motivated to bring his flock to pious belief.
But these are the best of cases. Veniality, pride, greed, and lust are not less common among the scholarly. The ability to convince people of your opinions is not statistically associated with righteousness by any standard. When your authority is unchallenged, it will creep out into the world, and into the daily lives of all that follow. Your petty disagreements become identified as condemnations of sin. What you dislike is evil. God is your friend, and all who deny it are enemies of God.
And great leaders of faith die. The mass of followers, who may have been led by a true exemplar of human decency, are now trained to follow. They have ritual, and they have habit. Soon they have a new leader. That person is far more likely to rise to power by reason of political skill than true dedication to principles of faith, whatever the faith in question might be.
People who truly take responsibility for their beliefs, and actions before God, and live by faith are not afraid to stand before the world’s judgment. They do not seek the approval of followers, or even to be followed. If the Bible, or Koran is the word of God, then interpretation by a mere man is obviously not authoritative, however educated the man might be. That is fundamentalism. Fatwas, and Papal Bulls, televangelist press releases, conferences of bishops, elections of elders, pronouncements by mullahs, epigrams of gurus, are the opinions of men. Those who follow these leaders in faith are authoritarianists. There is no shortage of them, in any nation.
Tris
“Don’t follow leaders. Watch parking meters.” ~Bob Dylan~