I think that we have to start off with a premise that Blanche is not operating " on a full tank of gas." I think it might be a bit on the crude side, but it gets the point across. There are so many issues and challenges in Blanche's own background that it is nearly impossible for the reader/ viewer to ask that she be presented in a "normal" or traditional manner. It's probably here where Blanche has to be the protagonist. Williams wanted to create a character where there is so much in terms of challenges and socio- psychological baggage whereby one had to see her in a variety of lights, where strict moral judgment was nearly impossible.
We can only begin to list some of these elements here, and in doing, so we can fully understand why there might be a desire to block out reality and to not see things in a "coherent" or "normal" light. The social world in which Blanche had been raised has become completely undermined and replaced by a new and industrialized social order that has buried the past. Contrast this with another great Southerner's line about the past when Faulkner says, "The past isn't dead and buried. In fact, it's not even past." If this is true, then Blanche has to deal with the emotional challenge of a world that is physically dead, but emotionally alive and vibrant. We know little of her husband, but there are implications that part of the reason the marriage failed was because he was homosexual in a social order that saw it as taboo. This had to have some level of impact on Blanche in terms of how she perceives herself as a woman, and might also help to explain why there is a such a bizarre and twisted relationship she has towards sexual conduct, one in which she rebukes Mitch's advance but is overtly flirtatious with a young boy. The rejection from her position as a teacher for the same reason also adds to her complex nature whereby a denial of reality is present. Even in general, there is an edge to Blanche, almost as if to indicate that the premise of a woman who seems to be so assertive and so independent is only doing so to mask a frail sense of self and a condition of living that is the complete opposite. Her experiences have warped or distorted her view of reality and her place in it because such experiences are examples of warped reality. I suppose that this is a way of saying that there is little hope for Blanche to see the world as normal, little way for her to be able to accept reality for what it is. Realty and consciousness have been so distorted for so long that this is actually normal for her. To ask Blanche to see the world as "real" implies that she is able to tell the difference. I am not sure Blanche is because of the intense experiences that she has endured. In no way would I say that Blanche has not been responsible for some of these, but I do think that she is the protagonist in the play because she represents what many of us are in that we have experienced love, loss, pain, futility, and a sense of the disjointed in our own consciousness and have had to reconcile reality with it. In assessing Blanche, I think it's nearly impossible for us to turn the lenses of reflection and refraction upon ourselves. Such a loaded condition makes her to be not just the protagonist of the play, but one of the most compelling characters around.