It's hard to say if Tennessee Williams was making any sort of conclusive statement about anything in "A Streetcar Named Desire"; the play ends with everything in a big mess and no-one getting what they wanted. Blanche is carted off to an insane asylum, Stella is distraught and angry at Stanley, Mitch is heartbroken; even Stanley, who has finally rid himself of his unwanted houseguest, can't be too happy about the way his wife is now feeling toward him.
It does seem that Williams was not very optimistic about relations between the two sexes.
Stella has a man who excites her, but he is abusive, and she feels powerless to leave him.
Blanche has a very romantic, idealized concept of love that she can never realize. Her youthful, poetry-writing husband turns out to be a closet homosexual. Her subsequent loneliness leads her to a series of promiscuous relationships that are emotionally unfulfilling. When she finally finds Mitch, who is interested in a more mature and complete relationship, it is too late. Although he is no moral paragon, he is repelled by his discovery of Blanche's escapades.
Stanley's interest in women seems to be merely animilistic. Although he usually gets his way, he must deal with the fact that his female companions are human beings who are hurt and angered by his brutishness, and then run away from him.
Like many authors, it would seem that Williams was looking around for some mature and happy model for male-female relationships -- a model that he could not find.