denial and self-hatred SPOILER
In his study of homosexuality in the movies, The Celluloid Closet, Vito Russo had this to say about Suddenly, Last Summer on pages 115-118.
According to Russo, Henry Hart wrote in the January 1960 Films in Review that
Tennessee Williams wrote the play Suddenly Last Summer on the advice of his psychiatrist. The doctor felt that Williams had for too long had disrespect for what was normal and should show homosexuality for the evil that it was. That would help him as well as society. This Williams did in his own wildly abnormal way. The pedophiliac Sebastian Venable's nightmarish end was a punishment for the sin of sodomy.
We don't see Sebastian's face. Russo compares him to horror movie characters like the creature from the black lagoon. He is not completely human, in a way.
Hart continued that the plot "exposes clearly the foremost causes of homosexuality." It "points to one of the horrible fates that can overtake this particular kind of pervert."
Russo also wrote about the problem persuading Hepburn to play Violet in the movie. He claimed that the director, Joseph Mankiewiscz and Spencer Tracy talked to her for hours in a vain attempt to convince her that there were such people as homosexuals.