The hypocrisy of Blanche's position is made very clear in the important dialog exchange about desire, both the concept and the street-car:
Blanche: What you are talking about is brutal desire – just – Desire! – the name of that rattle-trap street-car[…]
Stella: Haven't you ever ridden on that street-car?
Blanche: It brought me here – where I'm not wanted and where I'm ashamed to be.
Stella: Then don't you think your superior attitude is a bit out of place?
It is clear to both the audience and the characters themselves that they are discussing the streetcar Desire as a metaphor for the kind of desire that brings two people together. Each line of this exchange can be read in two ways – is Stella saying Blanche should drop her attitude as she knows she's not wanted at the Kowalskis' flat? Or that she should understand Stella's position because she too has felt crippling, damaging desire?
Blanche presents herself as a romantic throughout the play, clutching to notions of star-crossed lovers and gentlemen sweeping ladies off their feet. But when faced with a true love story, she balks. Blanche's kind of romance can't happen in the gutter. In theory, Blanche should see her sister's marriage as an epic love story between the princess and the commoner. But the truth is that Blanche's romanticism is a cover for the true cynicism of one who loves only calculatingly, for money and power and security. Of the DuBois sisters, Stella is the romantic.