How is A Streetcar Named Desire a tragedy?

I think that Williams' work is a tragedy for a couple of
reasons.  In my mind, the most overwhelming reason that the story is a tragedy is
because there is not a happy ending for anyone.  There is little in way of unity and
comedy for any of the characters.  Blanche is institutionalized, Stella recognizes that
she might have made a mistake only to be smoothed over by Stanley, exposed to be a brute
in the most savage of ways.  This is a setting whereby disunity and fragmentation
results for everyone.  I would say that another way the play is a tragedy is that it
reveals a challenging situation between cultures, different ways of life, where
validation is not really present.  Blanche is living in a different world, and it is one
that has passed her by in a brutally honest manner.  Yet, if Stanley represents the
force of modernity, one cannot take solace in that because any setting where someone as
harsh and as brutish as Stanley cannot represent a force of salvation.  In this light,
the drama reflects another tragic condition.