There is much about what might be the hidden justifications for immigration of all kinds, that can be found in old texts and in the kind of advice that is passed down through generations of businessmen and statesmen by word of mouth.
Here's one: In the 1700's, at the dawn of the industrial revolution, one of the wealthier class observed that while it is merciful that the people not starve, still it would be unwise for them to become to prosperous, for then they will not work hard.
And so we are flooded with immigrants, legal and illegal, lest salaries skyrocket because the people are too prosperous to want jobs or to work overtime.
Another was said by Voltaire, who painted a picture of Christians of all sects doing buisness with Moslems and Jews--all working harmoniously together because no one group formed a huge majority--in other words, he was touting the practical advantages to industry and government of "diversity".