Which the article addresses directly:
When looking at the more serious crimes like burglary and violent crimes, the Netherlands hold a spot in the middle. The number of murders in Amsterdam and Rotterdam is also this year the highest amongst the investigated cities, expect those in the US. This top spot on the list the Netherlands has to thank to the high number of liquidations in the drugsscene.
Summary: Amsterdam and Rotterdam have the highest murder rates in Europe, and they're largely drug-related crimes.
This is not at all unexpected -- drug dealing is a high-profit enterprise that is operated by folks who are demonstrably uninterested in the well-being of those they "serve." It's not too surprising that such folks are less prone to qualms about killing.
But it does tend to highlight the real weakness of the libertarian position, which is their unwarranted assumption that people will all be nice and polite if only the government would let them make their own bad decisions.
They still want cars, gold chains, earrings, tatoos, tvs, stereos, the latest in gangster apparel, etc. and they continue to commit crime to get it.
I would bet that condition does not prevail in the Netherlands, which has an extensive government health system and (I assume, since we do) antidiscrimination laws which in effect prevent landlords and perhaps even employers from testing for and penalizing drug use.
Also, it would be interesting to see which drug industries dominate the murder scene. From what I understand no drug in Holland is completely legal but some (marijuana, hashish) are decriminalized, which is not the same thing. Fully legal markets would allow the drug industry the same resort to the court system as other industries have. AFAIK no country has tried legalization in this sense,. although of course we did when Prohibition ended.