A few years ago, a professor at Pasadena City College led a class discussion on the famous story “The Lottery.” In the story, a seemingly normal village carries out a bizarre ritual involving human sacrifice. The professor, Kay Haugaard, had taught the story many times over the years and was anticipating the usual shocked reactions from her students. Instead, she found that she was teaching a room full of moral relativists who thought that the ritual might be all right “if it’s a part of a person’s culture . . . and if it has worked for them.” To Haugaard’s...