Weltschmerz ran deep at the New York Society for Ethical Culture in Manhattan in January when Glenn Lowry, the director of the Museum of Modern Art, and Elizabeth Diller, of Diller, Scofidio and Renfro (DS+R), defended their recently announced plans for the museum’s expansion. These have sparked controversy because they include razing the neighboring, now-empty American Folk Art Museum building, designed by Tod Williams and Billie Tsien, and purchased by MoMA in 2011. The vitriol from the local critical and architectural community has been raucous, ad hominem. The crowd at Ethical Culture wanted blood, to see DS+R taken down a peg, shamed. Why? To be sure, the quirky little building—which opened in 2001, just after 9/11—is worthy of defense: it is a beautiful and unusual work with the remnant scale…