When Ferruccio Furlanetto enters the room, he presents the calm, distinguished appearance of a member of the diplomatic corps. Only when he speaks—in the thoughtfully measured cadences of his sonorous basso profundo—does he hint at his actual calling. The seasoned 63-year-old Italian bass is back with San Diego Opera to sing the lead role in Ildebrando Pizzetti’s Murder in the Cathedral, an obscure opera (to American audiences at least) based on the T.S. Eliot play of the same name. Although this role of Thomas Becket, Archbishop of Canterbury, is one Furlanetto’s signature roles, it is more than mere coincidence that…