But violent media does desensitize people who consume it.
The ridiculous claim is that violent media can actively make people violent.

Desensitization works like this:
We have psychological barriers when it comes to harming other people. Violence is just shocking to us, and thus hard to commit.
On top of that, we have moral barriers: most of us believe it’s wrong to harm others and thus we do not do it.

Now violent media weakens those barriers:
By becoming familiar with scenes of violence and gore, we are less shocked by violence and thus, if we wanted to hurt somebody for any reason, we might be less hesitant to do it.
To be clear: Violent media would not make us WANT to hurt people, but it would make us less likely to resist those urges should we have them.

As for the moral barriers: media can teach us that sometimes violence is justified. The media doesn’t have to be violent to teach us that, but usually it is.
As an example, think of CSI: Miami and how Horatio Caine, the main police guy, regularly takes justice into his own hands and beats up a pedophile, a cop killer and on another occasion let another pedophile die when he could have saved him. The message sent by the media is clear: the worst criminals deserve to be beaten/die.
Now imagine Average Joe is watching this show. He believes killing is always wrong, that justice is up to courts and not members of the public, etc. he might even be religious.
He watches the show and he’s basically told “hey, society actually approves of killing pedophiles you know?”. His moral barriers weaken a little. After repeated exposure to such messages, his moral barriers weaken very much and he starts to wish death and child molesters.
Now that won’t make Average Joe go out to hunt and kill pedophiles. But if something happens in his life that makes him want to kill pedophiles (maybe one day his nephew is abducted by a pedophile), then Average Joe will no longer think “killing is wrong, even in the case of pedophiles”: his moral barrier will no longer be there.

So now you have Average Joe in the following state of mind:
– He has a reason to go out and kill people.
– He doesn’t think it’s wrong/immoral/disapproved of by society.
– He’s so desensitized to violence, he has no trouble shooting somebody in the head, stabbing him or bashing his skull with a hammer.
What’s stopping him? Maybe the law, but if he’s angry, depressed or in some other “I don’t care anymore” state of mind, it won’t stop him.

Now for this example we’ve been using people who kill child molesters, but it could be anyone or any reason that motivates a killer. The Aurora and Sikh Temple shooters both had reasons to shoot the people they killed.
So the motives of killers and violent people may vary, but what’s common to all cases is the fact that they aren’t sensitive to violence anymore, whether it’s psychologically or morally. These barriers that prevent us from slaughtering each other just because we can no longer exist in these people’s minds (or have been seriously weakened).

As a final note, it should be considered that media isn’t the only thing that can weaken our barriers. Morticians, coroners, surgeons and others who are regularly exposed to serious injuries likely become desensitized about violence over time. Of course just because they aren’t shocked by serious injuries or aren’t squeamish about using a knife on a human body doesn’t mean they’ll go out and kill people.
Police officers, who both experience violence and are expected to commit violence (such as shooting people in self-defense) can be desensitized both psychologically and morally (this can explain many cases of police brutality).
Boxers probably wouldn’t be squeamish about getting in a fight but they might have moral issues about it.
The list goes on…

In summary:
– Media makes us less likely to refuse to commit violence.
– Media will not give us killing urges, but it can make us less likely to resist those urges if we have them.
– It’s not just media that can do this – our job, sport or other things can do it.