Killing is a human function, it always has been.
The reason why you and people you know havn't killed is because of your abiding by the law.
Plus the possible fear of prison you may have.
HOWEVER - When society breaks down, killing for you will be a natural thing. Self protection.
Sure, you saw this under hurricane Katrina. The murder rates spiked.
But I dont agree that killing for the sake of killing is natural. It is usually done either protecting ones property, steal others property(including women) or to win dominance and create a new social order.
When the mafia kills it is to secure its dominance. Sometimes the mafia might have a trade monopoly in say the pizzaria business. There is suddenly a new pizza maker in town outcompeting the mafia. The mafia will then either get this guy to submit to their rules or they kill him.
