McCoy's counter argument is that the majority of kids grew up with violent images but became decent citizens or even conscientious objectors.
The story raises two important questions. One is whether exposure to violence in the media prompts us to behave violently. Of course it does. Every social psychologist would agree to that. But it only affects some of us, not all of us, in such a way as to lead to violent behavior on our part. Any two matched cities across the northern border from each other are likely to watch the same shows, but the American city is likely to have eight time the homicide rate of the Canadian city.
There may be a dozen or more easily identifiable things that create a predisposition to violence, and the media is only one of them. McCoy's position is that TV is unimportant; the Dershowitz figure's position is that it's the main determinant in the case.
That brings up the second important question. McCoy's position depends on free will. Some of us choose to follow the models we see on TV, while others choose not to. This gets us into metaphysics. (What the heck is free will?) And, if we dismiss free will, it gets us into a conundrum of a different color. If we can explain a behavior by identifying its environmental causes, is there any such thing as "guilt"?