Edit: Actually over a quarter.
Look at Germany. Look at France. Look at what's happen to Japan because such an option isn't as viable.
It's simply not politically feasable to say, "Without immigrants, our economy is f'ed."
And yet, that's what politicians in Germany are saying: "Denn Deutschland braucht sie dringend: Durch die seit Jahrzehnten sinkende Geburtenrate gibt es auch weniger Arbeitskräfte. Diese Lücke konnte lange über Zuwanderung aus dem EU-Ausland gefüllt werden. Doch inzwischen reicht das nicht mehr aus." (https://www.spdfraktion.de/themen/neustart-migrationspolitik, the social-democrat representatives in Parliament)
"Because Germany needs them urgently: Due to the declining birth rate for decades, there are also fewer workers. For a long time, this gap could be filled by immigration from other EU countries. But this is no longer enough."
To the detriment of their origin countries who suffer from losing their best and brightest. How "Northern countries exploit the South again" is a (rather quiet) talking point that I believe will become louder in the future.
