The average nonbeliever may know even less about his tradition’s intellectual debates than the average Christian does — because its institutions, like Sunday Assembly, tend to be tiny, relatively new and allergic to anything that resembles dogma. But nonbelievers should pay attention. Atheism, like any ideological position, has political and moral consequences. As nonbelievers become a more self-conscious subculture, as they seek to elect their own to high office and refute the fear that a post-Christian America will slide into moral anarchy, they will need every idea their tradition offers them.

Yet modern secular humanism is also a species of 21st-century liberalism, and many of its adherents have absorbed the modern liberal tendency to shy away from ideology in favor of a message of nonjudgmental inclusion. Mr. Harris worries about any secular humanist who upholds “tolerance, above all, as the master value,” he told me. “What that person doesn’t see is that these irrational beliefs he’s refusing to criticize are of huge consequence geopolitically and personally — and are themselves sources of intolerance.”

Today, nonbelievers often seem inclined to describe atheism and secular humanism as an “identity” whose claimants should focus on winning cultural acceptance rather than intellectual debates. Here, they are taking their cues from the civil rights movement, particularly the rhetoric of gay liberation. Some organizations, for example, declared April 23 the first “Openly Secular Day,” “a celebration of secular people opening up about their secular worldview, and an opportunity for theistic allies to show their support for secular friends and family.”