[godsinhisheaven]

I think part of it is, as the youth numbers decline, the culture declines with it. This is addressed in the video, people >18 and <40 are those who keep traditions and culture alive. If you somehow imported a bunch of babies who were raised in Korean families, Korean culture survives, and if you import a bunch of 60+ people, well they're not going to be spreading their culture as much as someone who is 30. But babies and the elderly aren't the ones immigrating all that much, it's the (relatively) young singles and families. If you somehow managed to keep up the current population of SK by importing only young Thai families, within 4 generations SK would be North Thailand. I think is only a small part of why many countries are resistant to immigration, and on the micro-level, it's as simple as asking, do you want more neighbors? Or less? And I think, generalizing greatly, most people would say less.