Furthermore, despite living in a rather conservative state (Arizona) I have never encountered a person with such a paucity of understanding. For this to comprise, then, roughly half of the nation?

Chances are you met one and didn't know it. My father once asked my (high-school-aged) neighbors how long ago the dinosaurs lived. They said they didn't know but guessed about ten thousand years ago. I was surprised, because I knew it was millions of years ago although I didn't remember exactly how many millions it was (but vaguely remembered the number 65 million in connection with dinosaurs).