“If there’s one thing I want you to get from these writings, it’s that White birth rates must change.” So reads the first line of the Buffalo shooter’s rambling 180-page message to the world (much of it plagiarized from previous mass-shooter “manifestos”). And through many portions of the document, 18-year-old Payton Gendron obsesses over women and their fertility, regurgitating right-wing talking points about the loss of white supremacy as other races fill America. He rants about “broken families with soaring divorce rates” and young people choosing not to get married at all. He frets over “sexual hedonism” and denigrates Madonna...