It is a far right talking point, or just right now I guess? But it also is a reasonable one. Not from the blood and soil only Europeans are American standpoint, but from the standpoint of having an increasing percentage of first generation immigrants. Japan has seen issues with this at the same time they have benefitted from it. It isn't a matter of blaming the immigrants, it is a disservice to them too. We can't welcome them properly at the rates that would be necessary to fully offset fertility decline. That doesn't mean we shouldn't allow any immigration at all. We should do it as quickly as we can do it correctly. And that would be true even without the demographic problem. Having one or two immigrants in a school is probably too low, we can go faster than that. Having half the class be new from varying places doesn't work. It is also a problem for the donating countries. South America can't afford for all their working age people to head to Spain, they are already hitting their own demographic decline. Africa is on the other side still. They have too many children relative to the working age population. Taking only working age men and not their children harms Africa in a similar way.

I'm not saying allowing immigration in a steady controlled fashion won't help, just that it won't be enough, and that the levels that would be enough aren't possible without impacts on the immigrants, their new countries, and their originating countries being severe enough they don't balance.

Right now the US has 4.1% of its population residing unlawfully. That is 8-20x any European nation. It is largely due to the federated system and a suspicion of national identity systems, but just being able to bring in the rate we have been, but correctly through the system would be a start.