Canada is a good example, where the anti-immigration narrative has become much louder very quickly. People get nervous/upset when they see their culture or population visibly changing.
Short-termism of our leaders will lead to a systemic collapse just like in the Soviet Union.
Uh, expand?
Immigrants quickly take on the fertility characteristics of the host population, because they are subject to the same pressures and incentives. So immigration has to be perpetual. In the mean time, the source countries' fertility is slowly coming down to and below replacement as well. So it can't last forever.
The only thing that is "solved" meanwhile is keeping wages depressed, which helps businesses. Allowing wages to rise might help improve native fertility.
Edit: I should note that in the last few years Japan has modified its residency laws. As well as getting hundreds of thousands of "technical trainees" (in reality, pretty much enslaved factory workers) from China and Viet Nam, it's also getting hundreds of thousands of caregivers from the Philippines, and, for some reason, Brazil.
So even Japan is accepting immigration these days, albeit very reluctantly.
https://en.wikipedia.org/wiki/Demographics_of_Japan#/media/F...
https://en.wikipedia.org/wiki/Demographics_of_Japan#Foreign_...
