Religion isn't necessary to explain this. I was raised without religion. Most people seem to believe that our actions define who we are. I tend to think that our thoughts are a better indication of our real self, given that our thoughts are less constrained than our actions.

Watching and reading about bad things doesn't turn you into a bad person by exposure, but if you enjoy torture porn then i'm going to infer that you enjoy thoughts of torture and sought out that which reflects your thoughts and that makes you a bad person in my view.