I see your point regarding Sweden... I was lucky enough to have travelled quite a bit and all over the world, and the "worst" of Sweden that I remember was drunk teens throwing up on some major street in Stockholm. Maybe they have some of that dullness about them that I didn't care much about, sort of like Germans, but even those things don't come near the level of agression that one can feel in a place like India, Africa or China or among Tamil Tigers... not that I've been to all of those places.
Just thinking out loud... (and certainly not trying to paint a any one nation with broad strokes, just researching the possibility that human agression may be directly related to parasites).
Bottom line: compare hot and parasite infested places with their opposite. Middle east vs. north pole. India vs. Hawaii. Somalia vs. Canada...