To allow, indeed encourage, unlimited mass human migration is such a foolish, indeed clearly suicidal, notion that it is surprising to find the idea politically dominant (indeed unchallengeable) throughout the West.
(The fact that some powerful special interest groups benefit materially from mass migration in the short term is insufficient to account for the phenomenon - ruling elites have seldom acted to destroy their cultures for their children; indeed the ruling elites have traditionally had by far the longest time horizons of any group. Planting trees for your great grandchildren to enjoy was not unusual behavior among the English aristocracy.)
Mass migration of humans fits well with political correctness's underlying ethic of unselfishness and the underlying hedonic evaluation: by-and-large PC policy is justified in terms of increasing the happiness/ reducing the suffering of the greatest number of people.
This is operationalized in policy terms as taking goods (material goods such as money; and social goods such as status) from the haves to give to the have-nots.
A swift way to achieve this is to allow or facilitate the migration of have-nots into the nations of the haves, where they will be entitled to an equal share of goods; or indeed an extra share of goods since they have suffered so much in the past, and to set-them-up for the future.
Logically this redistribution of people ought to continue until differentials in goods are removed and peoples' hedonic levels are (thereby) equalized - indeed potentially reversed, as a punishment inflicted on those who formerly had more than their 'fair share'.
The obvious rejoinder that the situation is unsustainable is given short shrift - since we don't really know for sure exactly what makes for sustainability of a society - and the suffering is immediate and present whereas possible futures are disputed and uncertain. Maybe things will turn-out fine?
The short-term-and-certain trumps the long-term-and-contingent.
Therefore, we should not refrain from doing certain good (i.e. redistributing goods) now merely for fear of what might, or might not, happen in the future.
And anyway, things are different nowadays, and the process of mass migration can be 'managed' so that everyone (or, at least, everyone who matters; everyone who deserves consideration) can benefit from it.
The role of the PC elite is therefore not to stand in the way of mass population migration from have-not nations to have nations... except perhaps when it involves the have-not elites leaving their nations.
The usual politically correct line is that the most skilled and expert segment of have-not populations ought to stay where they are, should indeed be forced to stay where they are if necessary and prevented from migrating to have countries - since that is the unselfish thing for them to do.
More people will (probably) be made happier and helped to suffer less if have-not nations force their doctors, engineers and computer scientists to stay-put.
But the poorest and most helpless mass of have-nots clearly benefit hugely and immediately (in terms of goods) from migrating to a wealthy place where they will be given preferential treatment over natives, and therefore they ought to be allowed to do this - as long as the process is 'properly managed' (by the PC elites of the have nations).
But there is a problem: the selfishness of the haves.
Specifically, the (non-PC) native population in the have countries will tend to resist the confiscation and redistribution of their surplus of goods - this presumed 'surplus' being (roughly) the difference in average per capita wealth between the have and have-not nations.
But this resistance is selfish - and selfishness is the ultimate PC sin.
(Indeed, the non-PC haves are the only real villains of the piece, the flies in the ointment - since everyone else is merely trying to do what is right and proper and moral.)
However, the trouble is that humans are intrinsically selfish; so the problem of the selfish non-PC haves resisting redistribution is not likely to be one that is going to go away...
Obviously, people should not be free to be selfish... obviously people need to be made-to-be unselfish... and yet who will guard the guardians?...
The politically correct answer is to take matters out of individual human control and hand-over the whole process to an impersonal bureaucracy with committee decision-making by vote.
The bureaucracy will then frighten, force, or defraud the (evil) non-PC haves into behaving unselfishly, as they ought to do.
(This will actually be good for them - although they may not recognize the fact.)
And thus the process may continue to completion, and much benefit may be conferred upon the world - and all by the PC elite acting altruistically on-behalf-of the have-nots, and managing the whole thing.