That assumes people have the ability for critical thought, which is usually developed in school. Schools in the US have not been doing well due to lack of funding, so it makes sense that the populace at large is a bunch of idiots.
Lack of funding isn't the cause.
Schools in the US receive more funding per pupil than schools in the EU or top performing Asian countries. More directly, the US spends more than Canada and gets far worse results. It's difficult to find the root of problem, but I would blame religiosity and widespread violent crime. Young earth creationists are still doing their best to hamstring the sciences no amount of money spent on a child can make up for a father who is dead or imprisoned.
http://news.gallup.com/poll/170822/believe-creationist-view-...
How could the educational system possibly be unaffected by most of the country still denying a foundational part of modern science?
Upon further investigation, we can see that it's not unaffected. Pitched battles are still being waged on intellectual ground settled generations ago in nearly every other developed country.
https://en.wikipedia.org/wiki/Creation_and_evolution_in_publ...
The reality is that only one of the above opinions, "God created humans directly in their present form" is provable/disprovable in any way and therefore the only one which science has anything to say about.
That said, 42% is still an admittedly high number. But you are the one who fails to understand a foundational part of modern science when you assume that correlation equals causation, and that increased religiosity results in poorer education while failing to realize that both are correlated with increased levels of poverty, which seems far more likely to cause poor education than religion.