Do you mean does art imitate life or does life imitate art?
Hmm... I don't care what people say, America was built on violence. Look at the Native Americans for example. Look at slavery and the Civil War. Look at the World Wars. Maybe we are more civilized but violence is just a part of the American landscape.
I also think violence sells. Most of the biggest grossing movies had some degree of violence. Deep in our souls we all crave a certain amount of violence.