Immigration is extremely important economically. New immigrants take jobs that average citizens wouldn't, and can provide a large low-income population base, which keeps goods and services flowing, where they could otherwise stagnate with a more settled customer base. Anyone that claims the opposite is just trying to obfuscate their racsim.
Japan has a 2.29% immigrant population. Then look at their work life balance.
Korea has a 2.3% immigrant population and you can see the terrible work life balance there as well.
The US has a 14.4% immigrant population and work live balance isn't great either. As if immigrants aren't a truly massive problem that the media makes you believe.
Both Japan and Korea have very specific cultures, and yeah, they screw their work life balance. IIRC Japan is currently working on changing that. But that's their culture - part of their nation - and flooding it with immigrants erases not only bad parts but also good ones. Hell, look at Germany that struggles with immigrants as far as I know.