Megan McArdle has a great footnote
Yes, anarcho-capitalists, I know about medieval Iceland. I do not think that the U.S. can be run on the same basis as a tiny, culturally homogenous island nation.Whether or not I agree with the article, this point is actually the most important one. The ability to make a diverse nation work depends on the rules of conduct.
I also read Icelandic sagas. It's unclear that things are notably better when law enforcement is private (some rather spectacular massacres occur due to feuds). International relations become a challenge -- unless we want a nation of privateers like Egil from Egil's Saga. After all, how do you enforce agreements between nations when all law is private the parties who negotiated the law are likely far away.
It's not that we cannot find ideas of value in medieval Icelandic culture, but that perhaps we should pay close attention to the actual problems they had as well.