I think it is less a true lack of intelligence. It is the people being trained (indoctrinated) by government schools to be blind followers rather than thinkers. They've been taught to recite what they've been told rather than to analyze the facts and come to a conclusion.

We used to teach people how to analyze and to think. Then they were taught what to think. Now they are taught how to not think. Much modern education, especially higher education, actually seems to make people dumber than when they started being "educated."