A dominant theme of A Streetcar Named Desire is the beginning of the end of the class structure, gender inferiority and superior status in America's "South" during industrialization.
The audience expects a demure, typical, Southern woman to reveal herself in the form of Blanche but it becomes obvious that appearances are deceiving. Blanche is the antithesis of herself and her opposing personalities will sooner or later expose her weaknesses and her neurotic temperament.
Blanche's fall from grace and ultimate hospitalization in a mental institution highlights the discrepancy between expectations and norms and Blanche's need to retain her imagined status despite her very real indiscretions. This reveals her hypocrisy and the reality of the time. Blanche's contradictory nature and her acknowledgement of her own inconsistent behavior which " brought me here—Where I'm not wanted and where I'm ashamed to be" will eventually destroy her, contributing to a cycle of violence from which she cannot escape. Blanche has no real concept of morality and her grasp of right and wrong is entirely questionable "when the devil is in you."
The underlying plot throughout A Streetcar Named Desire relates to society as a whole and its shortcomings and the confusion that abounds when conformity makes demands. People will always judge others and "casting the first stone" is very relevant here. It drives the audience's feelings for Blanche and whilst disapproving, Blanche is to be pitied as a product of her society.