As an American:
Those people you describe are not “classic American,” they’re ignorant, and they annoy other “Americans” as well you.
Or, they’re people who, because they’ve been exposed to many different cultures growing up, even if those cultures are “American” versions of the original culture, may feel comfortable talking about the cultures because they (at least feel that they) know a bit about them.
Or, they’re people who have been told what to believe, and so believe that, regardless.
Or, they’ve got opinions that they’re sharing to start up a conversation, and possibly get some feedback from others, to learn more.
Or countless other reasons to be talking about cultures they have no “right” to because they don’t “know.”
Thing is, they’re all still people, first, before being “American”—whatever that word is supposed to mean in this supposed-meltingpot-turned-supposed-saladbowl-mishmash,—and all of those things happen in all countries. (At least, I assume they do, but since I haven’t been to all countries yet, I guess I can’t say so… whoops I guess I’m doing it now haha ; )
I’ve got a circle of friends that are tons of different cultures and mixes of cultures. We talk about culture all the time, because it’s relevant in our lives and how we view the world. By sharing those viewpoints with each other, we help each other sort out our own true beliefs and identities from what we’ve simply absorbed from others.
But, as others have pointed out, to group all Americans, or all “classic” Americans into a group of ignorant talk-a-lots… isn’t that doing to the “them” sort of in a way what you feel the “them” do to other cultures?
Not saying all Americans are perfect angels, or all Americans don’t judge people by culture: some do and it sucks. The US and the people in it aren’t all bad.. no country or culture or group of people is all bad.