Once an intellectual taboo, atheism has become one of the great growth industries of the third millennium. Combative atheist titles like Christopher Hitchens's God Is Not Great, Richard Dawkins's The God Delusion, and Sam Harris's The End of Faith become New York Times bestsellers; faith-bashing films like Bill Maher's documentary Religulous and Ricky Gervais's comedy The Invention of Lying perform respectably at the box office; a Trinity College study predicts that nonreligious Americans (including atheists and milder skeptics such as agnostics) will comprise 25 percent of the populace by 2029. Factor in President Barack Obama's inaugural nod to "nonbelievers," which followed earlier shout-outs from former president George W. Bush(!), and suddenly atheism looks like an improbable cultural juggernaut.

But might the aggressive stylings of Hitchens & Co. — dubbed the "New Atheists" by friends and foes alike — undercut their own efforts to spread the gospel of nonbelief? Hitchens, for example, has stated that religion "should be treated with ridicule, hatred, and contempt." And last July, atheist blogger PZ Myers — inspired by an old anti-Semitic smear — drove a rusty nail through a communion wafer (considered the body of Jesus by Catholics when blessed), tossed both items in the trash, threw in a banana peel and some coffee grounds for good measure, and wrote about it gleefully in a post titled "The Great Desecration." (In a final flourish, Myers re-nailed the wafer to pages ripped from the Koran and The God Delusion.)

Among nonbelievers who see atheism as a movement, not just a private choice, there's some concern that these extreme tactics could backfire. When the Amherst, New York–based Center for Inquiry goadingly launched "Blasphemy Day" earlier this fall, for example, Paul Kurtz — the center's founder and emeritus chair — accused participants of "go[ing] beyond the bounds of civilized discourse in a pluralistic society," and compared their output to Nazi-era caricatures of Jews. This burgeoning disagreement is nasty enough that some participants and observers are using the S-word — schism — to describe it. Which, when you think about it, kind of defeats the atheist point.

Enter Greg Epstein, Humanist chaplain at Harvard University and author of the just-published Good Without God: What a Million Nonreligious People Do Believe (William Morrow). Depending on your perspective, Epstein — a youthful ex-rocker from Flushing, Queens, who boasts graduate degrees from both the University of Michigan and Harvard Divinity School — is either a combatant in this brewing civil war or a peacemaker who could save atheism from itself.

Tonally, Epstein's divergence from the New Atheists is sharp: he dreams not of decisively crushing faith, but of a future in which the godless and godly cozily co-exist, respecting each other's convictions and even making common cause on issues of mutual concern. Two years ago, this difference caused something of a crisis for Epstein when, prior to a conference celebrating the 30th anniversary of Harvard's Humanist chaplaincy, he distributed a press release labeling Hitchens et al. "atheist 'fundamentalists' " — a term which, with its dual charge of mindlessness and hypocrisy, is about the most incendiary term one nonbeliever can throw at another. An ugly row ensued, with Epstein claiming the phrase was misinterpreted and others rejecting that explanation. ("There really seems to be only one appropriate response," wrote atheist blogger and Epstein critic Brian Flemming. "Fuck you.")