Do you know about Maxwell's Demon? It's described this way in Wikipedia:
In the philosophy of thermal and statistical physics, Maxwell's demon is a thought experiment created by the physicist James Clerk Maxwell in which he suggested how the Second Law of Thermodynamics could hypothetically be violated. In the thought experiment, a demon controls a small door between two chambers of gas. As individual gas molecules approach the door, the demon quickly opens and shuts the door so that slow molecules pass into one chamber and fast molecules pass into the other chamber. Because fasterare hotter, the demon's behavior causes one chamber to warm up as the other cools, thus decreasing entropy and violating the Second Law of Thermodynamics. [link]And that is of course a fantasy concocted to show how entropy works. But the immigration version of Maxwell's Demon is also a fantasy, but it's accepted as a fact across the political spectrum, from the most (heh!) 'ethical' libertarian to the ditziest liberal to the most narcissistic neocon. Maxwell's Immigration Demon is, however, as much a fantasy as its thermodynamic original.
The idea is that some combination of diligence on the part of the Feds and Ellis Island emotionalism ensures that while many foreigners are a grubby lot who must be bombed constantly to keep them in line, foreigners who cross the magic border are, due to that demon, a wonderful bunch of people, much better, in fact, than Americans, and who should be encouraged to come here and replace said inferior Americans.
Read More: http://praxis-mag.blogspot.com/2015/12/maxwells-immigration-demon.html