As a cognitive effect from exposure to violent media,the victim reader/audience loses empathy slowly.Children below the age of 16 are especially affected by violent media as their brain is still under formative stage of development.
It has generally by found in most of the surveys that people who read/watch violent media,they are more likely to become violent during their lifetime or they might act violently in society.
So the social message to media is to stay away from violent depiction,more so because it affects children under 16 adversely and can make them criminals later in their life.