From actual comics. Duh. Joker in past times has been portrayed often as loving a sick joke, murdering hundreds of people regardless of age. However, he is almost always vain and egotistic (this trait is still present though unfortunately diluted) to the point where he considers himself the equivelant of an artist. I can see the Laughing Fish Joker killing whoever he damn well pleases, but the point isn't that he has any morality. No, the point is that he considers the usual petty criminals far below him. He is after all the Clown Prince of Crime, and why indulge in raping someone like a mere gutter crim when he could be sparring with Batsy on far more grander terms.
For many this is the ultimate interpretation and people should accept there are different opinions. I accept that people love the skinning raping suicidal Joker, more power to you when reading this book then. But I'll always find that route very forced and two dimensional. Killing babies souynds like a bad joke, which is why the finale of NML (apart from the crippled joke) was a bit of a letdown for me. That and the fact that it just HAD to be the Joker, give another villain the damn spotlight for once DC!
Also no way did he rapes Babs. The fact that no one has mentioned it in the comics is near proof.
