Americans aren't any dumber than anyone else.
I once witnessed a Canadian girl ask a guy what country Mexico City was in.
anecdotal evidence of a few dumb people in a place doesn't speak for the whole group. a good indicator would be comparing our test scores as a nation to other countries ( we rank pitifully by the way)
Much of that is padded in other nations.
I'm not going to argue that American schools are the best in the world, but having lived in America, Canada and England, and having traveled extensively in Europe, it is my opinion that Americans aren't any dumber than anyone else. Less informed about the world around them, maybe, but not any dumber.
We do, as a whole, tend to be short sighted. If the problem isn't fixed with a happy outcome in a 1/2 hour TV sitcom we're not happy and tend to loose interest.