I.e., the material interests, and specifically the Goulds, now function as the opposite of idealism. See Charles Gould's line during his disillusionment, concerning wealth: "There was nothing for it now but to go on using it." The message is that the material interests have lost their idealistic optimism, that they no longer inspire mankind with the faith of progress and betterment, that they continue in the modern world on automatic, as an amoral force for outward organization and behind-the-scenes conquest. Note the subtle zig-zag of Mitchell's designations, implying that the bank is on the same side of the street as the Casa Gould -- also opposite from the house of idealism.