I will agree that people often have an innate tribalism that causes them to want to like people themselves more without any outside information but I don't think educating against that is "propaganda" any more than any of the moral lessons we instill in children are. Even teaching children about cultural traditions or public behavior is, I suppose "propaganda" through that lens. I have heard Mr. Rogers called "propaganda" before for teaching children to be good neighbors. I guess "right from wrong" lessons are picked and chosen by parents and society at large and is all "propaganda" in that sense but I would personally argue empathy is the most important to being a good person.
I would also argue against your point that the US takes in the most immigrants because it is "empathetic" we depend on immigrant labor for both unskilled and skilled labor. And illegal immigrants are exploited in many industries (esp migrant farming and meat processing). Trump himself exploited cheap illegal Polish labor to build Trump Tower.
https://www.nytimes.com/2017/11/27/...legal-immigrant-workers-union-settlement.html
From the article:
"In 1998, Wojciech Kozak described to The New York Times the backbreaking labor on the job.
"We worked in horrid, terrible conditions," Mr. Kozak said. "We were frightened illegal immigrants and did not know enough about our rights."
Making illegals afraid is a good way to exploit them.
We are not an empathetic nation, we have some very troubled things from our past: Japanese internment camps, Tuskegee Syphilis trials, the Native American trail of tears just to name a few. Freedom of speech and religion are in our constitution, it has nothing to do with the "empathy" of our government since.
As far as your assessment that monocultures thrive more, it is I suppose easier to not have to deal with racial conflict if there are no different races to conflict but this doesn't apply to the US as it has always been a melting pot (and has benefited from that in terms of culture, the arts, and even scientific advancement), and the only way to change that would be what the Chinese are doing to the Muslims (ie committing war crimes and atrocities), so even if you would wish the US had only one national identity, it never had that. We were a nation of immigrants from the inception.
Black, Asian and Hispanic Americans are just as "American" as White Americans (though it can perhaps be argued that perhaps all these groups have less claim on what being American should be than Native Americans if a monoculture should be argued for it should be their culture)
Non-Christian Americans are just as "American" as Christian Americans.
Gay Americans are just as "American" as Straight Americans.
To suggest otherwise, is actually very un-American.