Advertisements bombard us with music constantly, and Muzak drips through shopping malls. It's hardly a secret. We can abuse anything if we have enough motivation. I don't think I understand the translation of your question. There are many bad things in our world, and a healthy person must come to grips with the evil that exists in the world.
Nightmares are a way for the mind to explore darkness in the safety of sleep.
B. Our sleeping mind can sense an unrelated physiological activation and might create a fearful dream to explain the sensations. But some people have serious difficulties with recurring nightmares, which could be triggered by a disorder like post-traumatic stress or possibly an obsessive fear. Wartime experiences can trigger nightmares for life. This situation can be helped with behavioral or medical therapies. Perhaps, though, I am not understanding your question, and you speak of humanity's tendencies towards violence in general.