Before he addressed the crowd that had assembled in the St. Louis Hyatt Regency ballroom last November, Lt. Gen. John F. Kelly had one request. “Please don’t mention my son,” he asked the Marine Corps officer introducing him. Four days earlier, 2nd Lt. Robert M. Kelly , 29, had stepped on a land mine while leading a platoon of Marines in southern Afghanistan. He was killed instantly. Without once referring to his son’s death, the general delivered a passionate and at times angry speech about the military’s sacrifices and its troops’ growing sense of isolation from society.