@Arkos
I don't think Thorfinn is being naive at all. He's just sticking to his ideal. Naive is being ignorant, he knows the dangers, but he's not willing to give up on his ideal for the sake of safety. Nor does he truly think it's a sword's fault that evil deeds exist. It's simply that when someone carries a weapon, they carry with them a sense of false assurance and/or aggression. I don't know where you live, but if someone has a gun in a holster and approaches you, it doesn't matter how polite they are, it creates a sense of unease. Now if that person sees you as a threat for any reason (real or imagined), their mind is going to swing immediately to using their gun. Now you suddenly have a hostile situation, which can cause violence over something.
Also, what you're saying isn't exactly true. True to history, the first settlers, both Scandinavian and Western European didn't immediately end up in a war with the natives as soon as they landed. It only started turning bad when the exploitation and oppression came in. The first people that come in contact with other groups of people are rarely people that are ready for war, they're usually explorers. Columbus is the worst example, but generally speaking, the first exchanges are peaceful.