What you say about Jenny could be true...you're right, not every woman goes insane and starts trying to kill their cheating husbands (but make no mistake they are out there!).
However, the fact that Jenny wanted to kill Quentin doesn't excuse him of cheating on her or treating her the way he did. But, to be fair to Quentin, [spoiler] later on, when Jenny's ghost returns to make baby Lenore well again, Quentin tells Jenny he's sorry for what he did to her and wishes that, if he could do it over again, he would do things differently. And I believed him when he said it....at that point I think he was truly remorseful over what happened between them.
I know Jenny tried to kill Judith with a knife and tried to burn Edward to death, but I can't say I have very much sympathy for either of them. As I said, locking her up in the tower room did more damage than good, and I think it drove her to the point of becoming more and more dangerous as time went by.
I like Beth but I can see why Jenny went after her....Beth had been her servant, her friend, and then she sees her in her husband's arms and kiss him...it was a betrayal on Beth's part and in Jenny's unstable mind, she had to avenge it. [/spoiler]