Late next month, atheists, humanists, freethinkers, secularists -- in short, nonbelievers of every description -- will gather in dozens of cities to mark the holiday they call HumanLight.

Whether by singing from a Humanist Hymnal, decorating a winter wreath or lighting candles dedicated to personal heroes, they'll celebrate what has been an exhilarating ride for the faithless -- a surge in recognition that has many convinced they're on the brink of making a mark on mainstream America.

During...