There is a dark side to religious devotion that is too often ignored or denied. As a means of motivating people to be cruel or inhumane -- as a means of inciting evil, to borrow the vocabulary of the devout -- there may be no more potent force than religion. When the subject of religiously inspired bloodshed comes up, many Americans immediately think of Islamic fundamentalism, which is to be expected in the wake of the September 11 attacks on New York and Washington. But men have been committing heinous acts in the name of God ever since mankind began believing in deities, and extremists exist within all religions. Muhammad is not the only prophet whose words have been used to sanction barbarism; history has not lacked for Christians, Jews, Hindus, Sikhs, and even Buddhists who have been motivated by scripture to butcher innocents. Plenty of these religious extremists have been homegrown, corn-fed Americans. Faith-based violence was present long before Osama bin Laden, and it ill be with us long after his demise. Religious zealots like bin Laden, David Koresh, Jim Jones, Shoko Asahara, and Dan Lafferty are common to every age, just as zealots of other stripes are. In any human endeavor, some fraction of its practitioners will be motivated to pursue that activity with such concentrated focus and unalloyed passion that it will consume them utterly. One has to look no further than individuals who feel compelled to devote their lives to becoming concert pianists, say, or climbing Mount Everest. For some, the province of the extreme holds an allure that's irresistible. And a certain percentage of such fanatics will inevitably fixate on the matters of the spirit. The zealot may be outwardly motivated by the anticipation of a great reward at the other end -- wealth, fame, eternal salvation -- but the real recompense is probably the obsession itself. This is no less true for the religious fanatic than for the fanatical pianist or fanatical mountain climber. As a result of his (or her) infatuation, existence overflows with purpose. Ambiguity vanishes from the fanatic's worldview; a narcissistic sense of self-assurance displaces all doubt. A delicious rage quickens his pulse, fueled by the sins and shortcomings of lesser mortals, who are soiling the world wherever he looks. His perspective narrows until the last remnants of proportion are shed from his life. Through immoderation, he experiences something akin to rapture. Although the far territory of the extreme can exert an intoxicating pull on susceptible individuals of all bents, extremism seems to be especially prevalent among those inclined by temperament or upbringing toward religious pursuits. Faith is the very antithesis of reason, injudiciousness a crucial component of spiritual devotion. And when religious fanaticism supplants ratiocination, all bets are suddenly off. Anything can happen. Absolutely anything. Common sense is no match for the voice of God...