Er, well, that was a poorly worded hypothetical question–I should rephrase…
People who uphold a strict belief that everything is either good or evil, “Sacred” or “Satanic,” are much more susceptible to propaganda (“Taking the Risk out of Democracy,” Alex Carey), and are therefore more likely to commit violence (whether they believe it’s justified is ignored in this statement).
(Just to clarify what I mean by propaganda [though it’s probably unnecessary]: I’m using the definition of propaganda, in this instance, that refers to information or persuasive messages that lead this “listener” to believe the “speaker’s” beliefs virtually at face value; I differentiate information as objective statements with no moral/political implications which are both open to interpretation and open to decision.)
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ha yes, we were discussing weather or not violent media or violent dreams could causes violence. then the conversation evolved to “What does cause violence?” So I guess in a way we are sort of still on topic.
The problem is that neither is good. 
Though… If you think that killing in dreams would be good and healthy, kill, it WILL be good and healthy, and there is no sense for anyone to prohibit it. If you think that it is immoral or dangerous, just don’t do it, because if you do, it WILL harm you, and you will have permanent guilt and avenger characters and so on. There is no sense for anyone to order or even advice you to do it, either. But if you know or feel or think that it is bad, or unhealthy, or harming other people, or dangerous for astral creatures, or immoral, but still do it… You are having a problem. Though I do not say you are ready to go on a killing spree in real life… Once a fried of mine, he is an amateur soothsayer, told me what the difference between the sin and the crime is. A crime is something that harms other people, and a sin is something that harms yourself, your own soul. But people are so different. For example, for some people killing a cockroach would be a sin. And for other people it would be a sin/crime to leave it alive, because it can crawl to the kitchen and bring microbes to food and plates, and so on… But if you kill it just because you like watching it dying, it is a sin, though nobody can prohibit you to do it.
Funny thing, but it must mean something… I wonder what they should do with people, who, when playing video games, shoot both enemies and friends, just to test a new gun… 
Human organism, its hormonal system and so on evolved slower than the brain and much, much slower than the civilization. Humanity created culture, and rules, and taboos, and religions, and laws, and great ethical systems… But when we feel offended, our brain sends to our body the same signals, that in times when the danger could be a saber-toothed tiger, or flood, or a big shaggy ape with a stone hammer… Not a boss telling you can be fired, you see… And the body prepares itself to a kill-or-run reaction; it still can do it, in spite of all our habits… When we want to leave the room slamming the door, that’s not our brain to want it, that’s our hands want, our heart, our lungs, all our body… 
But we do not slam the door, ‘cause we are so cultured and civilized, we close it accurately, though our heart is ready to break apart… Then we go to the bus stop. The last thing we want now is shaking in a close bus, we feel like rushing along the street for a kilometer, punching all the poles you meet, so that your body implements both of its desires… 
But how is it possible, I am such a civilized young man, with a black case in my hand… Or a girl on high heels and in a short skirt… No, I will go in a bus, then I gonna read a newspaper and read something about terrorists, or nuclear weapons, or ecology, or asteroids approaching the Earth… Then I will see a thriller… I have no time for jogging; I am not one of these clean smiling western people, dang, I do not want my neighbors to think I would want them to think I was perfect… 
While my body is lying in the bed paralyzed, with only the heart beating rapidly…