You don’t need to be a psychiatrist to know that the Highland Park shooter is sick in the head. His evil act is unfathomable, but he does fit a familiar pattern of mass killers: alienated young male stoners who appear to be in the grip of a distinctively American madness. Those who knew the 21-year-old suspect, Robert Crimo III, say he habitually smoked cannabis, a habit he appeared to share with young mass shooters, including at Uvalde, Dayton, Parkland and Aurora. Obviously weed didn’t make them commit their evil acts, but it may have scrambled their brains enough for empathy...