I think they are a source of bad behavior, not the end all but it isn't a coincidence that music, movies, and video games have gotten more violent over the last 40 years and real violence has also escalated alongside.
Those who have a good mental health upbringing are less succeptable to the *brainwashing* effect or influence of music, games, tv etc but I think we all are affected by it regardless to perhaps a miniscule extent depending on how much we *feel* our lives compare to the games and musics, movies portrayal of reality and perspective dealing with interactions between people.
A child with healthy role models and social interactions amongst others is fairly resistant to the effects of unrealistic social pressures these things put upon them through interactions AND peers responding to what is right (cool) and wrong portrayed in such.