Earlier quoted context omitted.
> Why would the solution to “our people aren’t having enough babies” be “we should import different people to have their babies here”? If you become poor enough and weak enough, you'll be "replaced" anyway. And not on your own terms.
It is not necessarily true, I think it is opposite. More poorer they get, less attractive that place becomes. Especially since Japan is not rich with natural resources, there is nothing really to steal there
They become more attractive to outside non-governmental powers looking to engage in economic arbitrage, which brings its own challenges.
They have less negotiating power with wealthier countries which impacts their sovereignty.
Poor countries also tend to have more internal conflict: https://gsdrc.org/professional-dev/poverty-and-conflict/
If we look at this empirically it seems clear that countries that trade ethnic sameness for economic prosperity end up more stable, peaceful and capable of directing their own affairs.
There could be some advantages to living in a country where strangers are also distant cousins, but they seem marginal.
There could even be emotional improvements for parts of the population who feel anxious about living near people who are genetically distant from themselves, but I've not seen great evidence of that. Particularly since ethnically cohesive but poor countries tend to fall into civil war regardless.
When you put it to the test and measure outcomes, there are tradeoffs that go far beyond giving up consumerism.