Thing is, all of Europe, most of the Orient, Russia, etc... All have the same problem. There aren't going to be enough people in "developing" nations to provide the immigrants, at least without emptying out entire countries, as even their birth rates are declining.
The way we're going, we're actually looking at global population decline in 50 years or so.
Which we (especially the global warming/climate change acolytes) should be celebrating. After all, if it's all us people and our toys that are creating the problem, logic would suggest that fewer people should equate to less of a problem.
In fact, twenty or twenty five years ago there was a movement called "Negative Population Growth" that was actively advocating for population reduction as the cure for a lot of society's ills.
https://en.wikipedia.org/wiki/Negative_Population_Growthhttp://www.npg.org/And what about automation and robotics? The United States used to be a manufacturing powerhouse, and "the arsenal of the free world." Look how many liberty ships we cranked out during WW2 to keep Great Britain supplied -- and how quickly we did it. Today I don't know if there are any civilian ship yards left in the U.S. We are hemorrhaging real jobs, so as what industries we have left continue to follow the siren song of automation and robotics, IMHO it only makes sense to NOT keep producing babies who will grow up to find no jobs.
And I don't think we need to import immigrants to compete with Americans for whatever jobs will be left.