It hasn't been that long since I transitioned into a Stage Four mode of faith, but it might as well be a lifetime for all the changes it's made in the way I view the world. Life certainly becomes more complicated when one begins acknowledging that the universe can't be neatly packaged in black-and-white categories, but at the same time I couldn't imagine ever going back to that earlier way of thinking.
Andrew Sullivan, in his book The Conservative Soul, gives an insightful look into the fundamentalist mindset and why it has become increasingly popular in recent decades. Although he doesn't reference James Fowler's Stages of Faith, the worldview he describes is that of most Stage Three individuals.
The appeal of fundamentalism is quite simple: seeking stability in an uncertain, ever-changing world, many Stage Three individuals naturally gravitate toward those who offer Answers (with a capital A) and who prescribe the security of a regimented life that's immune to the ambiguities of modern life. The fundamentalist mindset, so understood, is not merely the domain of certain Christian and Muslim sects, but can manifest in just about any religion, as well as in secular ideologies like Marxism.
For the fundamentalist, doctrine is supreme. Whether it comes from the Bible, the Koran or the Communist Manifesto, everything necessary for life has been spelled out in black and white and it is the duty of the individual to submit unquestioningly to that supreme authority. Realignment of one's life according to the dictates of doctrine is the individual's highest priority in life, whatever the cost.
If following the commands of that doctrine fails to produce positive results, then it is the individual who is at fault, without exception. If science presents evidence that appears to contradict some point of doctrine, then science is wrong, again without exception and without need to examine the matter further. Nonbelievers who live seemingly full and productive lives in contradiction to the warnings of doctrine are clearly liars and tools of the devil (or whatever the antithesis of good is according to doctrine), and are secretly quite miserable.
Freedom in a fundamentalist system is defined as freedom to do "the right thing;" one can never be free to do that which has been forbidden by doctrine. As Orwellian as that may sound to an outside observer (and even to fundamentalists of a belief system different than the one being examined at the moment), there is liberation of a sort to be found in the acceptance of strict boundaries.
The more that life can be reduced to a simple list of dos and don'ts, the less energy one has to spend wrestling over complex issues or worrying about how one's actions will impact others. "I'm only following orders" (which is what it boils down to) may not hold up as a defense in a court of law, but it nonetheless goes a long way toward assuaging the conscience when an action taken in obedience to God (or God's equivalent) causes harm to another person.
The "tough love" approach stems from the same mentality; any suffering that results from the administration of "tough love" is for the good of the recipient. Whatever means are necessary to force the "sinner" to repentance (and thereby save his eternal soul) are fully justified. Even death is preferable to living in a state of disobedience.
Not that it's enough for us to simply speak of fundamentalism in negative terms. Some individuals simply cannot thrive without a rigid structure to guide them, and some fundamentalists are genuinely kind people whose commitment to their faith drives them to make a positive impact on the world around them. At its best, fundamentalist religion motivates its adherents to give self-sacrificially for the benefit of others.
Unfortunately, the fundamentalist mindset all too frequently drives the faithful to seek ways to impose authoritarian controls on others, by whatever force necessary. Historically this has been no less true of Christians than it has been of Muslims or Marxists, generally speaking - and even today, some Christian sects advocate the death penalty for a laundry list of sins.
Perhaps it's inevitable that a majority of Stage Three individuals will see a moral imperative in forcing others to submit to the commands of whatever doctrine they hold sacred. Although the Christian Right is the most visible evidence of that mindset in the United States at the moment, one can see the same attitude among members of many left wing groups as well. In fact, it's safe to say that most causes are going to attract at least a few supporters who think in authoritarian terms.
All of that is not to say that Stage Three individuals should be viewed condescendingly by those who move on to Stage Four (and beyond); many such individuals are highly talented and successful, and many are actively involved in working improve the lives of those around them. And transitioning to Stage Four does not automatically make one a better person.
But the lure of fundamentalism is a strong (and sometimes irresistible) pull for those who view the world exclusively through the filter of whichever group they most strongly identify with. Escaping the fundamentalist mindset requires undertaking a difficult journey that cannot be forced upon any individual. Some are simply not ready for that journey, and others will opt to remain within their comfort zones.
However strong the temptation may be to try to push those in the latter group to "grow up," we risk causing more harm than good when we try to impose our agenda (however enlightened we may think ourselves) on others. In effect, we become the very fundamentalists we speak out against.
That doesn't seem to leave much in terms of solutions, but then again, if the world really was that black and white, fundamentalism would be the solution.