I'm no psychologist. However, it seems apparent that the media (TV, radio, the Internet) presents us with a picture of society, its norms, its mores, and what the landscape of society looks like – the biodiversity, if you will, of people: physical appearance, dress, and attitudes and beliefs; it's the source we use to figure out who we are. Saussure said there are no positive terms in linguistics, that we identify things by what they are not. Therefore, we need an external source to know who we are and what our values are - these things are not innate. That's what I believe.
Different cultures have different values, as is demonstrated by their respective media. Causality can be disputed here: is society reflecting values learned from the media or is the media simply reflecting innate social values? It has been shown via surveys that, say, Japanese children raised in the US tend to have the same values and attitudes as most US citizens despite coming from a culture with relatively disparate values. In less assimilated communities, say Chinatowns, the situation is more complex. On average, though, it's safe to say that many more in such places tend to speak their native tongues and keep their foreign values with a much greater prevalence. More to the point: our surroundings show us who we are by showing us what others are. Our relation to these others often dictate what we think. Society and the media socialize.
Then the question becomes: which one has a greater impact on socialization, the media or one’s own society? I don't think there's any right answer. Rather, I think it boils down to two key things. The first is whether society or the media is in a young mind's "Quality World," a phrase used by psychologist William Glasser in his Choice Theory to describe an individual's key sphere of influence and attention. The second is time, how much of it one spends with each influence. In this day and age, unfortunately, the media, especially TV and increasingly the Internet, is in many young kids' Quality Worlds, since this is how they know what the current trends are and can keep up with friends, and how most leisure time for them is spent.