I'm not aware of any cultures being completely homogeneous other than one in the Amazon, and that is at risk due to prospectors making inroads in the region.
In terms of this supposed hypocrisy you speak of, European countries invaded, colonized, and plundered far off lands. They imposed their culture and rules and mores while treating their vassals as mere chattle.
Immigrants to Europe used to be from former colonies or allies, hence Jamaicans and Indians in Britain, Algerians and Morroccons in France, and Turks -allies in WWI - in Germany.
In recent decades other countries started accepting immigrants, and a greater variety. While the excuse is humanitarian, the reason is not unlike the USA's: cheap labor and innvovation. Like the US, their spoiled kids don't want to scrub toilets and work farms. Unlike the US, their economies are anemic, waiting for the next big American thing to emulate, and only barely so.
Historically, wherever there are mixings of people, there are technological advancements, cultural developments, and economic growth. Even Hitler's Germanic purity ideal was dependent on invading other countries for the sake of prosperity. If Hitler succeeded and took over the whole of Europe and made it all German, within a few decades the wealth of thievery would be replaced by stagnation that would make North Korea look positively booming in comparison.
European arrogance was replaced by guilt, as well as reality. Don't treat immigrants nicely? You end up with the Brixton riots.
Japan is not homogeous, as minorities such as Okinawans and Ainu can attest. Nor are all treated equally. Same in China. Yes, their dominant ethnic culture is unabashadly supremist, but so were those in the West within recent memory, and still to this day to a large degree. Face it, Americans are Gods and everyone worships us, even the haters. And we know it. We walk around in other countries as tourists ye expect others to speak our language and cater to our needs.
THAT'S a large part of the threat to people and cultures I was referring to.
Europeans don't belong in the Americas anymore than Arabs do. The natives of this hemisphere are essentially culturally extinct, and racially disappearing also. The Ainu I mentioned in Japan, unique people. Try finding a pure one. Australian Aboriginals are being swamped out of existence while we complain about their British invaders being supplanted by Asians. The world has been becoming American, we're stamping others out.