Race vs. culture.
First of all, race has little to do with culture. The contingent relation of history from times when travel was difficult is all there is to it, and that’s practically over now that we have planes and ships and highways.
Next, immigration. You go to Japan, you’ll start adopting Japanese culture. I guarantee it. You are not going to spend a year there without learning to eat onigiri and taking your shoes off when you enter a private home. So a bunch of Koreans go to Japan, and wow, now there’s Korean culture in Japan along with Japanese culture. How could this possibly be bad? There’s nothing good or bad about national culture to begin with, but surely it’s good to mix in new elements that might expand your horizons if you are a member of the majority. And if Japanese culture is so flimsy that a population of less than 1% of Koreans will damage it, well, that’s the way it goes. Same thing for the 2.3% of people of Indian descent in the UK, or the 5% or whatever it is of all kinds of different mixed Muslim cultures in France. It’s just not a big deal.
And the tiniest, least important deal is American culture, which was never a single thing to begin with, which is based on wholesale genocide of natives and on a massive slave trade, and which was always very strongly mixed up with African, British, German, Dutch, French, and Spanish culture, none of which are all that similar to one another.