It's the whole idea promoted from the cradle to the grave that "stuff" ( money, goods, achievement, cars, houses, jewellery) are more important than people that causes the incredible sense of want and frustration that drives some people to commit violent crime, the massive drug abuse that we have and the high rate of muggings and robberies. We have ourselves to blame for that. We have a created a culture of people who are shown things and want things they can't easily have, so those who are none too bright and none too moral will use violence to get them, including murder. We have to adjust society's values across the board if we are to ever combat this at grass roots level. Even if we do that, you're very unlikely to be killed by someone you don't know, murders generally take place in a domestic setting and there's no deterrant for losing your cool with your family because in effect those are crimes of malice or passion.
"Terrorism" is a whole seperate issue, it's politically and culturally motivated and so cannot even be considered in terms of "normal" murder.
The death penalty also subliminally sends out the message that it's ok to kill. It is not ok to kill, anyone, for any reason, however much we might wish to on a personal level people who murder children etc etc etc, we have to set a better, less barbaric standard than affirming the killer's ideas that it's alright to kill, not to mention the innocent people that will be judicially killed because the law in this country is so lackadaisical.