What's true for a population need not be true for any single observation. Maybe you are all quite smart but collectively very dumb (the fallacy of composition works in both directions). Although I have always thought a better descriptor was ignorant rather than dumb...preserves both my faith in people (Americans) and the need for a good education system.
There was a line in train spotting that came after one character had been going on about how stupid and what wankers the English were and the other character finally said "where does that leave us [the Scottish] if we got colonized by wankers?"
It is a question the ROTW asks on a daily basis. Perhaps there is a relationship between the will to power and the will to stupidity (I believe in law they call this wilful blindness).
Nietzsche got at it this way:
"A sign of strong character, when once the resolution has been taken, to shut the ear even to the best counter- arguments. Occasionally, therefore, a will to stupidity". --FN Beyond Good and Evil--
I suspect Americans like Canadians are wilfully ignorant and that it serves to nip any cognitive dissonance in the bud. That is, the people are complicit. It takes a whole nation to get to Nuremberg!
Travis