[shiroiushi]

>America is much more welcoming of immigration, by which I mean legal immigration, than Japan or China. This is not in dispute.

It's not? It sounds like you know little about the world outside of America. Japan is stupidly easy to immigrate to: just get a job offer here at a place that sponsors your visa and it's pretty trivial to immigrate. Even better, if you have enough points, you can apply for permanent residence after 1 or 3 years, and the cost is trivial. In America, getting a Green Card is very difficult and costly, and depending on your national origin can be almost impossible. In Japan, there's no limits at all, per year or per country of origin, for work visas or PR. Of course, Japan is somewhat selective about who it wants to immigrate, but America is no different there, which is why there's such a huge debate about illegal immigration (in America it's not that hard; in an island country it's not so easy).