What are the disadvantages of Blanche in the play A Streetcar Named Desire by Tennessee Williams?

Blanche DuBois has many disadvantages. She has lost Belle Reve, her ancestral home. She has just lost her job as a high-school English teacher because of her predilection for seducing young boys. Therefore she has no money, no income, and no home. She has acquired a bad reputation in her home town of Laurel because of drinking, fornication, and other vices. She has been forced to seek shelter with her sister Stella, who is married to the animalistic Stanley Kowalski and is six-months pregnant. Blanche is getting older and losing her grip on her only option for salvation, which is to find a good man to marry her and support her. All these problems lead to another problem, which is her conflict with Stanley. He doesn't want her intruding in his household, and he knows instinctively, with a sort of animal instinct, that she abhors him and will cause him troubles with Stella. She and Stanley are enemies, but this is another great disadvantage for Blanche because she is weak where he is strong, she is broke and he provides all the money for the household as well as all the liquor, she is sensitive where he is insensitive, she is idealistic and romantic where he is a brutal realist. She can't help annoying him just by being there in the small apartment. She doesn't even have a bedroom of her own. When the baby comes, Blanche will be even more obviously in the way because she is taking up the space which will have to be used for the new baby. If Stanley were a gentleman he would try to accommodate her. If he liked her he would let her stay. But he is not a gentleman and he hates her and everything she stands for, just as she hates everything he stands for. The play is largely about the warfare between Blanche and Stanley, which she is bound to lose. She uses old-fashioned politeness, proper manners, good grammar, and all the armor of he upper class to shame him and to turn her sister against him. He uses direct aggression and deliberate vulgarity to make her look like a phoney.

The two antagonists seem intended to represent the Old South and the New South. Stanley. The Old South had polished manners and refined tastes, but their economy was based on slavery. Stanley senses that Blanche has more than one skeleton in her closet. He does some investigating and finds out why she lost her job and what sort of reputation she has in her hometown. In Scene Seven he reveals what he has learned to Stella:

Honey, I told you I thoroughly checked on these stories! Now wait till I finished. The trouble with Dame Blanche was that she couldn't put on her act any more in Laurel! They got wised up after two or three dates with her and then they quit, and she goes on to another, the same old line, same old act, same old hooey! But the town was too small for this to go on forever! And as time went by she became a town character. Rgarded as not just different but downright loco--nuts.

He destroys Blanche's one last hope of survival by conveying all this information to his friend Mitch, who was charmed by Blanche's upper-class pretensions and was about to propose marriage. Stanley completes his destruction of the sensitive, vulnerable Blanche by raping her while his wife Stella is in the hospital delivering their baby. Blanche suffers a mental breakdown and has to be taken to an institution, where she will live out the rest of her days.

The play is gripping because it pits two such different characters against each other. Blanche uses wit and words as weapons. Stanley uses brutality and vulgarity, of which he has an abundant reserve. We can sympathize with Blanche because, in addition to being the underdog, she faces problems we all face or will have to face in the future. There is no security in life. We are all in danger of losing our livelihoods. We all encounter enemies who threaten our relationships and our self-images. We are all growing older--and there is no cure for that. We would all like life to be better than it actually is. We would all like to be loved--but love is hard to find and harder to keep. When Blanche is taken off to the mental asylum at the end of the play, we feel somehow that we are going along with her. She is a tragic figure, despite all her faults. Stanley has won the battle. He has gotten rid of her. But we don't feel like congratulating him. Why not? Because he was bound to win. People like him always win.

A struggle for existence naturally follows from the high rate at which all organic beings tend to increase. There is no exception to the rule that every organic being naturally increases at so high a rate, that if not destroyed, the earth would soon be covered by the progeny of a single pair.
Charles Darwin, The Origin of Species 

The condition of man . . . is a condition of war of everyone against everyone.
Thomas Hobbes