Everyone loves the way Ledger portrayed the Joker. It was brilliant. Pure evil, and chaotic, but brilliant. Still, there is limits to how far a person will go. I dressed up like him for Halloween when TDK came out. However, that's as far as I went. You have to have your wires crossed to do something like this just because you're hard for a movie criminal. It's sick, and warped. Period. Anyone who would defend anything relating to Joker, and this mass murder is also sick, and warped.
Just my 2 cents for anyone reading that may try to rationalize it in the future. (AHEM!)