Do you believe that violence in media promotes violence in real life? Does media reflect cultural values or can it actively reshape them?
Both, probably. I do think that violence in the media promotes violence in real life by causing it to seem more normal. Studies have even shown this to be the case, such as if kids watch a movie about other kids being mean to each other they are more likely to do it themselves.
I think it probably works subconsciously that way for adults too, although adults are more likely to have a complicated psyche wherein these effects are likely strongest on people who were already violence-prone to begin with, which likely happens for a load more reasons than watching violence in the media. For example, I don't worry that The Husband likes to play what are in my opinion abominably violent games like grand theft auto...he's not going to go out and become a murderous car thief anytime soon. But I'll be darned if I'll let my 5-year-old even watch his dad playing it...
I do also think that there's violence in the media because it's what people want, however. Our culture is becoming more and more harsh that way. It's kind of sad that these things aren't shocking anymore. I count myself among this too, and I like series like Sons of Anarchy and 24 as much as the next person that have a lot of violence and stuff that probably would have shocked people 50 years ago. Dunno if there's any solution to this though. I wonder if industrialized civilization is in decay sometimes. I suppose the human race has always liked violence, given that the Romans liked to watch people mauling each other as well, but maybe the cycle is preparing to turn again when people get fed up with it.