Homosexuality
Sebastian is simply a different kind of person for his time, and is thought of lowly by some. Using Catherine as a sort of bait, he has forced relationships with the men that she brings in. This play showing what was done by Sebastian was wrong, the viewer needs to take away that it is not a blanket statement that all homosexual people are bad. Sebastian, warped by the views of his time, felt he had no other choice than to do what he did.
Judgement
Almost everyone in the play judges one another, and usually in the wrong way. Williams, when writing this play, was surely thinking it important for her to subliminally state that we, as a people, are too quick to judge. When Catherine is injected with a truth serum, Mrs. Venable seems to go insane, and thinks everyone is lying to her. Catherine may have misinterpreted the doctor as well, thinking that he would never believe the truth. Like in the real world, many events are misinterpreted, causing huge problems.