Even with a straight face, my jaw drops a foot at (1) the ignorance of most Americans, (2) their total unawareness that they are ignorant and (3) their ability to inculcate this ignorance into immigrant populations who then become just like them.
For (3) to happen there must be powerful influences at play in American society that, for a society supposedly based on individualism, produces a uniformity of thinking that would be the envy of any religion.
Perhaps it would be useful to explore them.
One of the most powerful anaesthetics (and aphrodisiacs) is of course the notion of American "exceptionalism" which says, basically, "we are smarter and more powerful than you". It began with the start of American imperialism in the 1820s, 30s and 40s. The is now a patent absurdity but, since it did not ask immigrants to abandon their cultural heritage, it was easily overlaid (rather like a duvet) and became a vastly comforting message for new and old.
There are other reasons.
What do you think they are? Religion? Materialism?
PS: my dentist is from South Carolina. So I always take a gun to my appointments.