Thomas Piketty has taken America’s liberal establishment by storm. Piketty is a French economist who has written a lengthy (577 pages) study, “Capital in the Twenty-First Century,” intended to provide a powerful intellectual justification for attacking the super-rich. Surprisingly, “Capital” hit No. 16 on the New York Times’ best-seller list for hardcover nonfiction books — a considerable feat for an academic treatise that, though clearly written, is no page-turner.