(Agreed about the immigration rationalization though)
Um, as far as immigration. You may have noticed that some countries are much nicer places to live then others, i.e., some have low crime and highly functioning economies and others are poor crime filled hell-holes. Why is that? Is it that something about being north of the Rio Grande magically makes people more productive and less prone to commit violent crimes? <\sarcasm>
The main reason is the people and culture of those countries. Thus if you import too many people from a different country, the pleasantness of the country to live will depend on the the nature of the new people. Notice that this argument assumes nothing about the role of nature versus nurture.
The main reason is the people and culture of those countries.
Both Koreas are ethnically and culturally the same. What makes one a SF near-utopia and the other a starving disgrace is the accident of having fallen within opposite spheres of influence during the Cold War and the subsequent development of radically different political systems. One could argue something similar happened with pre-unification Germany. I've read somewhere that the relative poverty in rural Southern Italy and wealth in industrial Northern Italy mirror the North-South dynamics of Reconstruction USA.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.