What to make of the career of Jann Wenner, who is selling the magazine he founded, Rolling Stone, capping a remarkable career in publishing? In the Age of Trump, we are instructed to admire successful businessmen, those who have, as the president likes to put it, “built a great company.” Wenner is nothing if not that. In 1967, he borrowed $7,500 from his family, including his future in-laws, about $50,000 in contemporary terms. Wenner is a child of privilege (he was a few years behind Maureen Reagan at the Chadwick School) and that loan was nothing to sniff at, but...