If you accept that the language, ethnicity, and culture are valuable parts of that country-
Such a country can assimilate some number of immigrants each year while remaining mostly unchanged. The immigrants learn the language, the culture, and marry into native families.
But as you increase the number of immigrants, the country can no longer assimilate them. They don't all learn the language, they don't know the culture, they form social cliques with other immigrants from the same country. They begin to change the face of the host country.
Personally I've never been thrilled by immigrants who say "Elbonia sucks, let's go to another country that is better and make Little Elbonia".
Things change. That's called life. To assume all nations and all cultures remain static over time is absurd. Hell, the nations as they are defined today are a very recent phenomenon. Some have only existed for a few decades!
The host country will become a new, different, more diverse country. That doesn't mean the culture of the host country is completely destroyed. Altered, yes. Destroyed? Almost certainly not.
And the detrimental effects can be mitigated if the host country works to actively integrate (note, integrate, not necessarily assimilate) immigrant populations, rather than isolating them through xenophobic policy and politics. It's the very fear of change that exacerbates the challenges of immigration.
As an aside, your characterization of immigrants as from "Elbonia" coming to make a "little Elbonia" is precisely the kind of xenophobic tendency I'm talking about. I'm sure folks said the same thing when Little Italy or China Town showed up in New York City, and yet today those areas are considered cultural jewels, contributions to society rather than infections that must be dealt with, components that have been integrated into a modern American identity.
Maybe don't assume immigrants are foreign invaders and they'll be more likely to integrate rather than isolate...
So your argument seems to be "that damage is part of life, deal with it". That's fine, I was just trying to answer your question:
damaging in what sense?
I don't assume all immigrants are foreign invaders, thank you very much. On the other hand, I have known some immigrants who expressly wanted to get rid of the people in the town they had just moved to and import their old country's people, culture, and government. That's not my characterization, that's what was said.
China Town et al are great because they are integrated. You don't have to be from China to go there. But not every immigrant wants to integrate. Does that mean we repel all immigrants? No! Does that mean we embrace every immigrant no matter what? Also no. I see no reason to welcome people who want me gone, and say as much to my face.
It is possible to understand both these realities at the same time. We don't need to get all black-and-white, "all immigrants are evil" or "all immigrants are God's gift".
I have known some immigrants who expressly wanted to get rid of the people in the town they had just moved to and import their old country's people, culture, and government
And what percentage of immigrants do you suppose those folks actually represent?
Are they really such a large group of people that they could actively "damage" a culture? Are they really so large a group that they could actually "dilute" the culture of the host country?
Again, I already concede, dealing with unintegrated immigrant groups is unquestionably a challenge (though it's notable those same challenges occur with local minority populations and the poor). You'd be a fool to believe otherwise.
But this narrative, that small, homogeneous countries are in danger of being overrun by an immigrant horde hell bent on reinventing their home country within the borders of the host nation strikes me as nothing more than rhetoric, a caricature, and nothing more.
Ultimately, I agree, immigrants are neither evil nor "God's gift". They're just people. Some of them are good. Some of them not so much. But I'm willing to bet the vast majority don't have cultural occupation on the top of their list of personal ambitions. Like all people they have more important things on their minds... jobs, family, food, a roof over their heads, those basic things that we all have in common.
"There's not enough of those types for them to cause damage" is not an unreasonable line of argument. One could argue it's OK to admit them because they will get nowhere.
The "immigrant horde hell bent on reinventing their home country" is not the narrative I was trying to present. I was mostly talking about the simple fact that a small homogeneous country that admits a very large number of immigrants (of any type, wanting to integrate or not) will be unable to integrate them all without experiencing significant change, which is concerning to some people. (You have already shared you believe it is a real effect but 'too bad'. I am clear there)
Such a country can assimilate some number of immigrants each year while remaining mostly unchanged. The immigrants learn the language, the culture, and marry into native families.
But as you increase the number of immigrants, the country can no longer assimilate them. They don't all learn the language, they don't know the culture, they form social cliques with other immigrants from the same country. They begin to change the face of the host country.
Personally I've never been thrilled by immigrants who say "Elbonia sucks, let's go to another country that is better and make Little Elbonia".