I will say that our society has become too desensitized, but I still put the blame on irresponsible parents not paying attention to what their kids do or watch.
I got tired of this blame music, movies and video games thing quite some time ago. Only time I agree with those finger pointers is when it comes to really young kids, kids who are in kindergarten and a few years older. Major violence is something they shouldn't be exposed to at that age, but when it comes to teens, even young teens(we're talking about PG13 movies of course)it comes down to the parents and how they raised them.
Also, if they want to start watering down PG13 action films now, well, say goodbye to a lot of them in the future considering more and more studios are shying away from R rated material due to not being able to make more money when the younger generation can't see those films.