I wouldn't say Americans are necessarily any stupider than the rest of the world. We've just been taught to be uneducated. Our public school system has been dismantled because there is no Cold War anymore where we feel like we must compete in all areas against Russia. Even more money is going to the richest rich; even less money is going to the poor; the middle class is dwindling-- and money has a severe effect on education, including self-education. And we are also in a climate where bimbos and babes on tv have become the intellectual role models of our youth, so rather than trying to achieve their full intellectual potential, girls are just trying to see how short they can get their skirts while still technically wearing clothes, how buff the guys can get with or without steroids and other performance enhancers, how crude and obnoxious they can get (which are apparently now valued traits), and how much stuff they can buy and collect over their lifetimes. We're also founded upon a nation-- not of democracy and freedom-- but of capitalist pigs who will do anything legal or otherwise to make a buck-- and the government has almost always been bedfellows in this. The government-endorsed capitalism is nothing new; we've been like that since the industrial revolution.
I hope the rubberband starts pulling back the other way though, because this whole attitude of "I don't give a shit about anyone but myself" has sickened me for quite awhile now. --Not everybody is like this I should mention; there are a few bright stars amongst the empty blackholed heads of the space cadets. But there are certainly enough people who act like the above that I really hope something changes soon and for the better.
