“The common good.” The phrase may sound out of tune with the harsh tone of America’s public square. But it crops up in Patrik Jonsson’s story today about professional work and citizen alertness. That’s what led law enforcement to Luigi Mangione, who has been arrested on weapons charges and is a suspect in the killing of UnitedHealthcare executive Brian Thompson. Many people anonymously and darkly cheered him on. But Patrik’s sources said that Mr. Mangione may have underestimated something else at work: a deeper respect for the common good.