The grainy black-and-white television ad shows a young girl in a flower-filled meadow, holding a daisy and plucking its petals, which she counts one by one. As the camera slowly zooms in on her eye, a man's solemn countdown replaces hers. At zero the little girl's eye is engulfed by an atomic mushroom cloud. As the inferno roils in the background, President Lyndon B. Johnson's voice intones, "These are the stakes -- to make a world in which all of God's children can live, or to go into the dark. We must either love each other, or we must die."

In this thought-provoking and highly...