[stcredzero]

Often used argument arguing against immigration.

That's a very shortsighted view. One can do an examination of world history and geography to strongly support the conclusion that commerce and cultural interchange has a tremendous amplifying effect on the strength of culture and the value of human capital.

Japan itself is an example of this on a smaller scale. When Europeans first got to travel in Japan, they marveled at the sheer volume of commerce they saw.

If cultural evolution is anything like genetic algorithms, then what's needed for optimal progression is a balance of interchange and continuity: multiple populations with some degree of interchange.