Media most certainly does affect behavior. Why else would advertisers spend billions of dollars on advertisement if they didn't not just think but know their appeals would affect the public's behavior? Not just violence but sexuality, the embrace or rejection of values, political persuasions and interests on a wide range of subjects and not just TV but all media has that potential.
I have a friend who made a near tragic decision when he was just 16. I don't know the full story but he somehow came into possession of a handgun. One day he found himself is a stupid altercation with another teenager over a dumb basketball game that escalated. It ended with him put the gun up the the other kid's head and pulling the trigger. Thank God despite being at point blank range, in the scuffle the bullet missed. What he said motivated him was his favorite gangster rap song that he couldn't get out of his head that glorified guns and shooting someone.
FYI: A happy ending. After spending his late teens in juvi jail, my friend had an encounter with Jesus, got married, is a devoted dad to his 4 kids, speaks to groups of at risk teenagers, is planning to record a rap/reggae CD and works as a Gospel radio personality.