I think that aspect of the problem is perhaps overstated. We are by no means crowded, less so farther north. We are also a long way off from equatorial zones being uninhabitable. Besides, by denying would-be immigrants a chance to pursue their own freedom, we may be unintentionally preventing the next great mind(s) from having the chance to advance our civilization. Legal, on-the-tax-role immigrants are NOT something to ostracize in my opinion. The problem with most Americans' mentality is that they only know of the illegal, non-taxpaying immigrant stereotype, and so they froth at the mouth any time someone mentions loosening immigration restrictions. It's absurd.