Do you believe that violence in media promotes violence in real life? Does media reflect cultural values or can it actively reshape them?
Yes...I think it can greatly influence violence in real life.
When you were little, before you'd lose that "innocence" you'd had as a child, what opened your eyes to the reality of the world? Your parents? Friends? An act of cruelty?
Seeing the violence and anger on TV and in the news opens people's eyes, perhaps disrupting the peaceful image we once had. It can give people ideas. I imagine schoolwide shootings were uncommon many years ago, but once someone had done it, it's now a nearly common thing.