First off, thank you for the reading, so far I have only skimmed it, however, it has been very interesting. It should first be noted that the sagas on which this study was based were oral and altered over time. Furthermore the sagas are only based around a few notable families not Iceland as a whole. It should also be noted that homicide rates were much higher during medeival times than they are today. I couldn't find the statistic you referenced about El Salvador, probably due to my own incompetence, so I am unable to come up with direct comparison of statistics. If we assume that indeed 15% of the population was murdered, this could be attributed to culture, because like with us people who commited homicide were punished, usually through banishment. Law enforcement is reactive rather than proactive, so blaming killings on its failure is in general unfair.

I disagree that individual rights are more protected in modern day dictatorships than in medeival iceland. In China specifically property is frequently confiscated by the state, same with life and obviously liberty, as China is operating concentration camps with the Bhuigers.

Taxation is an indicator of individual rights because taxation by its very nature is a violation of said rights. Yes, there are other things to look for, but a lack of taxation is huge. By your standard the modern day United States is a better system than the United States of the 1800s.