If 'Breivik' happened regularly, even just every three years, then I would see your point. A society that produces a Breivik (i.e. some crazy fascist who thinks killing the most children he can is what he should do with his time) every three years must indeed be sick. For these reasons I'm currently also concerned about most European countries.

Desth rate statistics don't do justice to the looming threat of a group/tribe/clan/haggle of people who are out to just kill out-group people no matter what. I'm not concerned much about the risk itself, but I am about what it does to civic life.

Norway's massacre rate is on par with the US when you consider that Norway has 1.62% of the US population.

This whole thread started with me saying that police overstepping their boundaries is one reason I wouldn't move my family to the US. Obviously that doesn't just apply there though. The massacre thing was brought up as a weird counterargument - which I'd file as a typical case of whataboutism. I agree that massacres aren't a good reason against the US, and for that matter one would rather avoid many western European countries atm if at all.