While it seems to be the case that teens watching almost anything, including gang culture films, can quite often be effected by watching them, this is usually only in the short term.
Let's look at a play by William Shakespeare which is all about street gang culture and violence. It also happens to be about two lovers, each of which belongs to a different and opposing street gang.
Romeo and Juliet by William Shakespeare
http://uk.youtube.com/watch?v=0LjuLSZU4Hk&feature=related
We must always bear in mind that the older generation, of which I am a member, quite often subscribe to the idea that the past was somehow better when in fact it was not.
Back in my youth there was as much street violence as there is today, problem is the old seldom want to believe that.
Mods & Rockers of the 1960s
http://uk.youtube.com/watch?v=o4LuoPh2Ku4
Teenage boys want to fight - the trick is to try to control this and organize them in boxing and judo clubs etc., where they can work off all that testosterone aggression.
For myself, I joined the British Army at age 15 and by the time I was 18 and ready for the Man's Army I was as fit as hell having slogged across Dartmoor in the rain, clambered over the mountains of Wales and canoed up and down miles of rivers at night. It leave little time for a punch up.
Only one thing to add though.. .my neighbour told me yesterday that her two year old grandson Charlie had thrown one of his shoes at her. Cannot imagine where he got that idea from! Can you?