Spoiler inside: What is it about Madeline/Judy that makes us forget...
...that she's a murderer?
That she didn't herself physically kill Elster's wife is immaterial; she was a co-conspirator.
Judy was Gavin Elster's "side girl", and really nothing more to him than that, though he clearly made her believe they were going to have a life together. He needed her to believe that in order to use her.
Regardless of Judy's motivations, she and Elster plotted and carried out the murder of his wife together. Once it was done he dumped her, knowing she couldn't talk.
So why is it, then, that we tend to view her with sympathy? Is it simply because she has genuinely fallen in love with Scotty, and he with her?
I like to think that much of it is due to Kim Novak's nuanced performance. We see her as a victim, even though she went into the whole manipulation willingly and with eyes wide open.
What do you think?