Ok so person A kills a person because they feel like it, person B goes after and kills person A because well reasons are not required in your uncivilised world. This really annoys person C who kills person B until eventually there is only one person left, revenge is not the only reason people murder each other. I understand that there is corruption, I understand laws change over time and I understand that the people who write the laws are fallible but laws are required if you plan on living in a group larger than your immediate family, they are usually there to protect you from others and others from you, you may not be the strongest person in the community.