AMERICAN EVANGELICALS are frequently bewildered by the aggressively hostile responses they elicit from the ideological left. Someone offers a generic prayer before a high-school football game, asking God to give the players courage, determination, and good sportsmanship. Immediately someone becomes apoplectic, as if America was on the verge of recreating 16th-century Europe's wars of religion. Soon, a civil liberties organization files a lawsuit to halt hazardous public piety.

Okay, that's a caricature. But good caricatures have recognizable features. Anyone who reads the newspapers will recognize the way some ideologues panic in the face of public religious expression and run to the courts to check the innocuous and perhaps beneficial pieties of the majority.

Sociologist Alan Wolfe's newly published book, The Transformation of American Religion (Free Press), is addressed in part to these panicked leftists. Calm down, he says, and lay off the lawsuits. Americans may be pervasively religious, but they are not in the aggregate dangerously religious. Go to India if you want to see that kind of religion.

Evangelicals might welcome a book like this. But unfortunately, this argument, designed to calm the Left, is disturbing for believers. Liberals should relax, Wolfe says, because the conservative Christians' rhetoric of biblical inerrancy and moral stringency is belied by their actual practice. Wolfe subtitled his book How We Actually Live our Faith, and he paints a picture of a privatized religion that lacks confidence and is eager to avoid offense.

This toothless evangelicalism, Wolfe says, is the result of market forces and peculiarly American cultural habits. "Christians and Jews … have ignored doctrines, ...