I disagree that Americans are stupid, for not all are. It's just that the stupid ones give us who are decent a bad reputation. 'Most Americans are stupid' would have been a more accurate post.
Everyone has their place on the bell curve - Americans tend to be poorly educated - because the populace allows it. If the school system spent more money on scholarship and less on gladiatorial contests, the situation might improve. However, as long as most US citizens continue to speak only one language - and that poorly, I fear the rest of the world will see us as not too bright.