People* are dumb.
Why?
They have been breed like that for many generations. Because all the classic Civilisations and Empires needed lots of dumb workers and peasants who were able to do their simple work, but not smart enough, to organize any opposition against the current empire.
And this in many different forms, from total slavery to all kinds in between.
Now with the Hypothesis, that smart people don't want to get exploited, they would rise up sometimes, where they grew in numbers - and got beaten down and crucified, hanged, quartered, etc. - so strong selection pressure for smart people not born into the elite and not wanting to become a monk.
Now with all that being said, I believe it is probably more a cultural mindset of "stupidness" than "stupid" DNA in the people, because smart people also keep their heads low and pretend to be stupid, when they can't win a fight. But this got into a habit of not wanting to think. So the solution to all the complex problems in the world I don't think is a super government, thinking for all their dumb sheeps, but rather smaller systems, less complex - and letting people get smart again, by giving them the opportunity to make decisions again about their life. Not just a allmost meaningless vote which allmost counts nothing among the millions of other votes, but voting the decisions down at their very local lifes. When you have to think for yourself, you will start thinking again. And then you don't want those decisions taken away from you. Thats only comfortable when you forgot how to do it.
* with "people" I mean the average person in the street, the one from the famous Churchill quote