I think that you have a very strong starting point here. It seems to me that you might want to lay off the colon use and just word it to be a bit more direct in what you are trying to say. Something that popped into my mind would be that "In his short story, A Lady's Beaded Bag, Tennessee Williams argues that a part of human nature is the social classification of people on the basis of wealth." A similar way to approach this would be to bring out the "class system" in the thesis statement. I would say away from the idea of "hope, desperateness [sic] and opportunity" because I think these are going to be brought out in the body of the writing piece. Williams is a writer who is able to bring out the social dimensions of people's interaction in class systems or other forms of stratification, and when this is brought out, I think that the emotions that are alluded to in the first part of the thesis statement would become evident.