Some of the motives for killing in the early Icelandic culture differ from the motives that people have today. For example, one motive to kill men in that time would be to protect oneself. It was very easy to kill. The men did a lot of traveling, sometimes alone. They would travel many miles in open spaces because of the lack of trees in Iceland.
Any man has an opportunity to attack the traveler and get away with it.
It was very important to carry weapons so that you could protect yourself should the need arise. Murders took place most frequently during the time of the Althing, when most of the men where away from home. Killing to protect oneself somewhat justifies the actions that these men took. The laws concerning murder weren't very tough. Another very strong motive was honor.