Somebody please e-mail a copy of the McKinsey Global Institute’s new report, “Farewell to Cheap Capital,” to Paul Krugman and Ezra Klein. Krugman, a New York Times columnist, and Klein, a Washington Post blogger and cable TV talking head, are among the nation’s more voluble deficit deniers. Citing the currently low yields on U.S. Treasury securities as a sign of investor confidence in the nation’s fiscal integrity, they argue that cranking up federal spending to stimulate economic growth is worth the risk of continuing to engorge the national debt.