Television and movies are typically trying to push the envelope and sensationalize things to make them more thrilling. Even the evening news sensationalizes news stories, to get more viewers. People who watch television can become desensitized to what they see, and, while most people will not act in accordance to what they see, it may impact a few rare people who are more vulnerable to committing acts of violence.
Television may cause some extra violence, but as a whole it is a result of the society that we live in. Over the years there has been more sex and violence on the television. This is not because they are trying to make the world more violent or sex more acceptable, but rather because our society has become more accepting of both as entertainment.
No, tv does not cause violence, because violence has always existed in the world. The first murdered was committed by the son of the first people who have ever lived. Cain most certainly did not have a television. Violence has existed, along with wars, since long before there was ever television.
Video games and televisions don't cause people to become violent in the majority of cases. In reality, some people are predisposed to being more angry and violent than Others. These individuals will be violent no matter how much television they watch or whether or not they play any violent video games.
TV does not cause violence in society. I think if anything it is a result of having more violent people in the community. If people are not able to handle seeing the violence on a show and understand it isn't real than that says something about the person, not the general population.