Think about Blanche's role in the play - She's the fly in the ointment, the wrench in the machinery and the source of the play's conflict. She shows up at her sister Stella's home uninvited and unannounced to sponge off her for the rest of the play. Okay, everyone needs help now and then but does Blanche show an atom of gratitude? No, that narcissist takes up the center of the stage, hogging the bathroom and the liquor, and expects her pregnant sister to wait on her hand and foot. She never tries to get a job or her own place and when she's not demanding sympathy or the red-carpet treatment, Blanche runs down her brother-in-law, Stanley because she and Stella had "superior" childhoods. Even if this is true (and one of the things we learn about Blanche is her propensity to lie) Blanche's upbringing gives her only the veneer of gentility, not the substance. She's a dishonest, lazy, manipulator who seeks out grown men for gain and teenaged boys for sex. She can't be trusted around innocents of any age and her perpetual role of victim warps the people who would help her along with those who resist her game. She almost deserves what she gets.
So who, between these two, who is Streetcar's villain? (The only other alternative is Stella, the sister/wife torn between Blanche and Stanley in the play's tug-of-war.) Neither character is malevolent by nature, only incredibly self-centered and driven. Given her background and lack of resources, Blanche's only developed survival skill involves manipulating the kindness of strangers. Likewise, Stanley's defense mechanism is to smash anything that manipulates or threatens his spot in the world. So, in some ways, the outcome of the Streetcar is set when Blanche boards the bus for New Orleans, well before the curtain rises. This is the story of flawed people on a collision course driven by compulsions they can't sense enough to change.
Maybe that's why people are still interested in this play, almost seventy years after its first production. Because of their flaws, Streetcar's characters are people, like the ones we see in the mirror. None of us are Stanley or Stella or Blanche or Mitch but we share some of their weaknesses and strengths. To one degree or another, we are all inadvertant bystanders, victims, and predators, still searching for a moment of Grace.