Mass movements can rise and spread without belief in a God, but never without belief in a devil,” wrote Eric Hoffer in The True Believer. “Seeing Islam as ‘Evil’ Faith, Evangelicals Seek Converts” is the headline of a recent New York Times (May 27) report by Laurie Goodstein. “Evangelicals have substituted Islam for the Soviet Union,” the article proclaims. Make that “some evangelicals.” All find Islam theologically deficient, but most do not demonize it. Indeed, the National Association of Evangelicals is making efforts to treat Islam with respect.

Goodstein cites notable militant evangelicals who call Islam “a very evil and wicked religion” and Muhammad a “demon-possessed pedophile.” They instinctively understand Hoffer’s assertion, whether they have read The True Believer or not. I would like to formulate a version of Hoffer’s observation, which I will arrogantly call the Hoffer-Marty Law of Movement Success: “Religious institutions decline if they do not have a clear foe to fight.” I urge sociologists of religion, political scientists and social psychologists to test it.

During a half century of Soviet communist threat, conservative American religious movements (and not only they) named communism the devil. Their opposition to this devil helped them to grow and flourish. When communism imploded, such movements floundered a bit, and looked about for new candidates. They tried “secular humanism,” “liberal churches,” “the New York Times,” but none of these fit the role of devil well. In the eyes of post-9/11 conservative Christians, Islam now can and will.

This column rarely focuses on the militants Goodstein too broadly calls the “evangelicals.” Instead let’s change the focus to “mainline Protestants” and test the new law on them. In trying to account for mainline Protestantism’s decline in numbers, scholars and polemicists have theorized, analyzed and scrutinized with ever diminishing returns. They’ve explored the effects of social and demographic change, of theological liberalism, of failures in nurture and formation. One can extend the list indefinitely without coming up with a definitive answer.

The Hoffer-Marty Law leads me to this hypothesis: what held mainline Protestantism together was anti-Catholicism (responded to in kind by Catholic anti-Protestantism). Fear of a Catholic takeover motivated liberal Protestants, including our editorial ancestors on this journal, to organize. Some Protestant ecumenical efforts promoted unity to help churches amass power over against Catholic encroachments, real or imagined.

Pope John XXIII and the Second Vatican Council worked for aggiornamento and friendliness between “separated brothers and sisters” and Rome in the 1950s and ’60s. Lay and clerical embrace of the new-style Catholicism deprived mainline Protestants of that unifying and motivating bogey—Hoffer’s “devil”—and left them without a vivid enemy.

Oh, yes, mainline Protestants murmur against “the world, the flesh and the devil” as these appear in many cultural manifestations, but they do not mass forces against them. They fear and despise militant Islamic fundamentalism, but are casually Islam-friendly. They grumble about but don’t demonize the Christian right—at least not to the extent of mobilizing forces against them.

Those evangelicals who do call Islam wicked and Muhammad demon-possessed know what they are doing. They know how to organize and mobilize. I hope mainline Protestants don’t take lessons from them.