I have no problem when filmmakers depict acts of violence. Nor do I have a problem with filmmakers depicting acts of extreme violence. I don't even have a problem with filmmakers depicting acts of sadistic violence. What I do have a problem with, and this goes for Kick-Ass in a most exceptional way, is when filmmakers depict sadistic violence and then positively reaffirm it for the audience.
There is plenty of sadistic violence in Schindler's List, but it is a beautiful, brilliant, good film about the horrors of what man does to man. There is some sick sadism in A History of Violence, but that film is ultimately anti-violence. There are plenty of sadistic villains in the James Bond films, but such a thing is designed to put the audience against the bad guys and for the good guys. Even when Bond himself turns ice-cold in his use of violence, it never makes the audience feel good about it. If anything, it makes me slightly afraid of the hero.
What Kick-Ass does is show a little girl brutally slaying a room full of criminals, with which I would not necessarily have taken issue, but for the ones she kills who aren't even putting up a fight, and the expression of glee on her face as she does so, and the way the audience members around me seemed to be enjoying it. Put all these things together, and it makes me sick.
(Criticisms such as these are also why I think Crank is one of the filthiest movies ever made and is one of, if not the worst movie I've ever watched.)
I'm still not sure how I feel about Kick-Ass as a whole. There is a lot about it that I really appreciate, but I can not and will not get on board with thinking there is anything good about treating sadism so lightly.