I was in a large, packed room in the Hilton. A conference held in June by the Cato Institute and an Argentine free-market think tank, Libertad y Progreso, had entered its final hours. Elon Musk had just spoken — remotely. Now self-styled anarcho-capitalist Javier Milei, Argentina’s president since December, had turned up, clad in a suit, not his trademark leather jacket, and, considerably calmer than his reputation, was giving a speech…