CMV: Mass media can influence one's behaviour. People only (justifiably) say otherwise because they don't want that to be censored.

Mass media has certainly been shown to influence one's behaviour. The 'Notel' study in Canada in the 1970s showed that residents in a town with no television were better thinkers, more creative, and more individualistic; then when television arrived, children became more violent and performed no better than the average, and people began acting in societal norms.

It's not a leap to extend this to things like violent video games, music with certain lyrics or connotations, the behaviours people see on TV or on the internet. When they see other people doing something and getting away with it, they have experienced that, know of it, know how to do it, know what it means, and know that other people - be they better or worse - can do it. The only reason why people monolithically cry out against it is because they fear that their video games and TV will be censored, which it shouldn't necessarily.