Why watch violent films?

When I watch a violent film (action/horror, doesn't matter), I'm fine until the part where someone is doing bodily harm to another person. At that point, I feel as if I am at the scene of a crime, and I feel only the need to stop it from happening. I know it's not real, but this feeling I get seems to be innate, and I simply cannot understand why anyone would want to watch something that displays crime in such a realistic way. It seems to me that if you do enjoy watching it, then you would have no problem watching it happen for real, or perhaps performing the act yourself. Perhaps, those who indulge in violent films/tv shows do not have a firm grasp on reality. Why does this protectionist instinct not show up in everyone who watches a violent film? Why is it so hard for someone like me to think of what I am watching as just a film? And why is it that most of the people I know who watch violent films on a regular basis have a very rude personality, and swear all the time? Personally, I think that violent films cause people to devalue life. If I have to watch a violent film all the way through, I am usually left feeling depressed, as if I have suffered the same kind of loss as the fictional characters have. It's the REALISM of it. Maybe my imagination is too vivid. Help me out, here!