How does the immigrants' experiences lend to Sinclair's argument toward the end of the book for Socialism?

This is very similar to your last question. Sinclair conceived The Jungle as a Socialist novel. The plights of the novel's protagonists demonstrate the evils and corruption of unrestrained capitalist economies. Jurgis and Ona Rudkus, as well as their immigrant friends and family, live in dire poverty. Their lives are at risk when they go to work, if they are able to find work. These conditions are the result of a company that seeks to maximize the speed and efficiency of labor with no regard to how such methods of production affect the lives of workers. The novel is a sustained argument that workers must gather collectively in order to assure rights and dignity for all individuals.