Yes, I think that due to too much television violence that it is rubbing off badly on children. I think that children are way too exposed to violence on tv, and need to see less violence so that they are aware of how the real world works and without knowing all the violence.
Yes, television violence harm teenagers, because teenagers are influenced by the things they see. Teenagers see violence on television and they believe that it is normal behavior. They believe that they can do the things that they see because they see the people on television doing the behaviors. It warps their perception of reality.
We know when we should do like we see, we are able to distinguish from right and wrong. We know we're not supposed to repeat what on TV and movies if it harms someone else. As for kids it's a different matter but the question clearly stated that it asking about teenagers.
Violence on T.V is not the best for kids but it certainly does not hurt them or influence them to do anything. In some citations it can help a kid or a teenager who is trying to be abducted by someone. If they use those violent techniques to get out of the citation that is at hand then that is one less kid taken by someone.
You are not and I believe that it actually helps them in some cases. Think about it. When your a kid every thing Is safe and you believe that nothing can hurt you. But believe it or not that's not how the world is, there are many people that are starving, and dying and they will hurt you no matter what. I believe if parents keep there children ignorant of the real world they are being blinded of the truth.