I feel that the explosion of violent entertainment doesn't so much come from our "inner need for violence" but our "inner need to be active". Humans, like all animals, are active by nature, and our current society (I'm speaking from an industrialized U.S. point of view here) has all of these "time-saving devices" (which really in the long run don't save time), which takes all of the activity out of our lives. Our society has become so concerned in making life "easy" and "safe" that it has also taken the fun and activity out of our lives. To satify our brains, we fantasize about things which really are no longer feasible in our society, and hence movies, video games, plays, books - entertainment media.
But I also agree with truthseeker, violence becomes a spiral in nature. Our aggressive human nature, begets such violent media, which begets more aggresssion, which begets even more violent media, etc. (notice how each action movie tries to outdo the previous).
-Xenu