More (not so) fun facts:
54% of American adults read below a 6th grade level.
21% read below a 5th grade level, which is considered functionally illiterate.
High immigration numbers don't fully explain it either, as first gen immigrants only make up about 1/3 of those with low literacy.
You sound like a real asshole. Jumping to conclusions about someone based on a single conversation is stupid, because it's not enough to know them. Try giving others the benefit of the doubt more, and maybe you'll find them less intolerable (and others will find you less intolerable as well)
As an example, my initial reaction to reading this is a cringe so intense that I feel it in my bones. Despite this, I am willing to give you the benefit of the doubt before letting that reaction tarnish my opinion of you, as I truly do not know you IRL, and there's always more to a person than what they can present to the world. There's also a lot that gets lost when communicating through text, so I'll reserve judgement. I'll just end this with a quote from the great philosopher Curtis James Jackson: