Peers also teach them. Children are taught by their friends and parents that fighting and killing is the only way to end a dispute. People do stupid things in most cases because they don't know any better. In order to become more intelligent and thoughtful, one must explore and understand many different ways of thinking, even if they're undesirable or evil. Only by understanding and accepting the evil will one strengthen the good side of himself.
Denial is destructive.
It is important to recognize that our desensitizing to the murders and rapes that we see in the news is a natural reaction. It is our attempt to deal with such problems without breaking down completely. We must accept it or else we'll get more frustrated as we see more crimes being committed. This is how we survive through all the evil things happening out there. We have not become desensitized because we see fake death on television.