how is blanche a tragic heroine in a streetcar named desire
In Tennessee Williams's A Streetcar Name Desire the character of Blanche is a self-centered, hysterical and wild-natured woman who has lost every possible chance of respectability and, as a result, has fled to her sister's house in New Orleans to, perhaps, create a new life for herself.
However disparate and immoral Blanche's life is, there is an element of pathos in it. All through her life, Blanche has been trying to escape suffering. When she loses her father's estate of Belle Reve after his death Blanche makes it clear that it was she who had to stay behind trying to bring normality back while Stella had already eloped with Stanley.
The reason why she uses her body as a method of obtaining benefit is not necessarily because she is a cheap woman but because, being brought up as a Southern Belle in a much safer environment, Blanche is raised with the understanding that it is perfectly fine to flirt and to use charm to obtain benefits from it. Now, away from the safety and old South charm of Belle Reve, Stella and her mannerisms are thrown into the lion's den of a very superficial and materialistic society. She has to survive the heartbreak that comes as a result of finding out how different the world is outside of Belle Reve.
Moreover, Blanche is very protective of her sister, Stella. She does hope for a better life for the two of them. She simply has reached the end of her rope and there is no way for her to fix anything.
Therefore, Blanche's story is meant to cause pity and not anger. The audience will, at some point, identify with a moment in time with her main problem: That society takes away the world, as she knows it, and throws her into a world that she is simply not prepared to live in.