My goal in writing this book has been to help close the door to a certain style of irrationality. While religious faith is the one species of human ignorance that will not admit of even the possibility of correction, it is still sheltered from criticism in every corner of our culture. Forsaking all valid sources of information about this world (both spiritual and mundane), our religions have seized upon ancient taboos and prescientific fantasies as though they held ultimate metaphysical significance. Books that embrace the narrowest spectrum of political, moral, scientific, and spiritual understanding - books that, by their very antiquity alone, offer us the most dilute wisdom with respect to the present - are still dogmatically thrust upon us as the final word on matters of the greatest significance. In the best case, faith leaves otherwise well-intentioned people incapable of thinking rationally about many of their deepest concerns; at worst, it is a continuing source of human violence. Even now, many of us are motivated not by what we know, but by what we are content merely to imagine. Many are still eager to sacrifice happiness, compassion, and justice in this world for a fantasy of a world to come. These and other degradations await us along the well-worn path of piety. Whatever our religious differences may mean for the next life, they have only one terminus in this one - a future of ignorance and slaughter.