It's not so much what the son's club represents itself that's important, but the contrast between the son's club and the underground city. You could talk about the son's club featuring fit, healthy, young enthusiastic people with positive facial expressions and their light costumes. Then on the other hand, the worker's city features a dark and crowded environment with 'mechanical' men devoid of gestures, heads bowed down etc. It's basically Lang's interpretation of how capitalism has divided society into unequal upper and lower classes.