Similar to the "Time Machine," the worker's city is far below the Earth's surface which is gloomy and robotic. The workers are inferior and only useful as part of a machine. If perhaps they are injured or even killed, the work must go on and no real regard for the loss of life is represented by the owner, "Freder's father". It is disheartening when the father says, "such accidents are unavoidable." The "people" of Metropolis have no compassion for humanity, and they feel that the workers are just subservient creatures that willingly perform ludicrous duties.
Eventually, the scientist produces machine men that will make "no need for living workers", but what will happen to all of the living workers? I do not think that we should become a society run by machines and robots. There will always be people willing to do working class work, and could probably do it better than a robot that may default like the Maria robot. I agree with the movie that it is important to include "heart between brains and hand." It is imperative to not take advantage of workers, because they will revolt as in "Metropolis." Although Freder proclaims that "ten hours can be such torture," it obviously does not need to be that way. Also, the storyline of the people meeting in the catacombs to hear Maria speak and search for a mediator reminded me of a Union meeting and Freder (the mediator) as the Union Steward.
I noticed that there was a star on the scientist's door. I don't know if that was a pagan reference or something anti-Semitic. I just found it to be interesting considering it was a German film.