Nicholas Schliemann is basically the voice of socialism at the end of The Jungle. He lays out everything: wage competition keeps workers from organizing for their own benefit. Big businesses own a monopoly of the money in this country, so the little guy can't get ahead. He points out that economic hierarchies also mean that women are subject to discrimination. He sees the only real freedom for women in a socialist state.
Schliemann also believes that socialism should only regulate the economy and not art. Art should be the product of people's leisure time, and everyone will have the right to participate in whatever art they choose once their work is done. Because there will no longer be a profit motive, there will be no time wasted on marketing or on mass production. We will only make as much as we need to get by. So everyone will have plenty of free time to do whatever they want to do, if it's art or writing or sitting around.
Jurgis is incredibly moved by Dr. Schliemann's vision of a socialist heaven, and we the readers are supposed to be, too. "Dr. Schliemann" is Sinclair's way of making a direct pitch to the reader to vote socialist in upcoming elections so that we can all achieve this wonderful cooperative future.