What are the cause and effects of media violence?

Conflict is an integral part of just about every story.
Violent imagery causes a reaction in the viewer. It gets the viewer personally involved in the plot. What effect does it have on the viewer? That differs from person to person based upon their personal disposition to violent acts.

If you’re asking if violence portrayed in popular media today causes people to be violent, I would say no. If a person claims to have committed a violent act as a result of something they saw in a movie, I would dismiss as rationalization. That person had a previously existing bent toward violence. We are creatures of free will.

Cause:
audience.

(Main) Effect:
more violence.

I agree with @The_Compassionate_Heretic. The cause is definitely the audience.. violence and sex sell.. but while they may desensitize audiences to violence.. I don’t think it’s drastic enough to actually cause violence to occur without some other major catalyst…

“Cookie Jar” by Jack Johnson

I would turn on the TV but it’s so embarrassing
To see all the other people I don’t know what they mean
And it was magic at first when they spoke without sound
But now this world is gonna hurt you better turn that thing down
Turn it around

“It wasn’t me”, says the boy with the gun
“Sure I pulled the trigger but it needed to be done
Cause life’s been killing me ever since it begun
You cant blame me cause I’m too young”

“You can’t blame me sure the killer was my son
But I didn’t teach him to pull the trigger of the gun
It’s the killing on this TV screen
You cant blame me its those images he’s seen”

Well “You can’t blame me”, says the media man
Well “I wasn’t the one who came up with the plan
I just point my camera at what the people want to see
Man it’s a two way mirror and you cant blame me”

“You can’t blame me”, says the singer of the song
Or the maker of the movie which he based his life on
“It’s only entertainment and as anyone can see
The smoke machines and makeup and you cant fool me”

It was you it was me it was every man
We’ve all got the blood on our hands
We only receive what we demand
And if we want hell then hell’s what we’ll have

And I would turn on the TV
But it’s so embarrassing
To see all the other people
I don’t even know what they mean
And it was magic at first
But it let everyone down
And now this world is gonna hurt
You better turn it around
Turn it around