Okay, so atheism isn’t exactly a new idea; indeed, it’s humanity’s oldest or second-oldest theological theory, depending on how you play the chicken-and-egg game with belief and unbelief. But you have to go all the way back to late-Victorian scoffers like Robert Ingersoll and Mark Twain to find a moment when celebrity skeptics enjoyed the sort of mass-market success that ours—from Christopher Hitchens and Sam Harris to Daniel Dennett and Richard Dawkins—are enjoying in America today.

In part, the vogue for atheistic tracts reflects the talents of the tractarians in question. But it also reflects the slow but steady growth of America’s secular demographic, and its newfound self-consciousness. The post-9/11 moment, in particular, seems to have made unbelievers feel unexpectedly embattled, besieged by fundamentalists both abroad and at home. And there’s nothing quite like a feeling of embattlement to forge solidarity—and sell books.

In this sense, the new mass-market atheism is following the same pattern as the Christian Right before it, which likewise drew strength from a sense of embattlement and persecution. These mirror-image movements can be seen as backlashes against the genteel secularism of mid-century, with its faintly condescending respect for the idea of Religion, and its studious indifference toward actual belief. This backlash has made debates over religion more polarizing than they used to be—and also more interesting.

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