The Society for Ethical Culture was an apt setting for Tuesday night’s conversation on the Museum of Modern Art’s forthcoming expansion. The plan to add 40,000 square feet of gallery space to the museum’s Midtown campus has charged a virulent debate about ethics in the architecture community. Ever since the museum and its architects, Diller Scofidio + Renfro, confirmed on January 8 that the expansion comes at the cost of the adjoining Tod Williams Billie Tsien-designed American Folk Art Museum building, which MoMA purchased in 2011 and will demolish before June, architects and critics have called foul on the institution and its builders for failing to respect and preserve the distinguished work of contemporaries.