if we look at governments as the local administrative function, then certainly, it shouldn't really matter to the government who its citizens are as long as they contribute to public kitty for the mutual benefit of the residents. and from that perspective we can see migration as enabling a kind of healthy competition between governments. one that's very empowering to the citizens. its a nice picture.

but governments apparently have roles which are not directly related to collecting taxes to lay sewers, and I think we should maybe be questioning those. and of course there are economic consequences to the population varying, and things start to unravel at both extremes of density.

from this perspective the US was a very good competitor in the attraction of talented citizens. sadly we won't really have a good accounting of what was lost.