This thread is in part about imigration, because immigration is responsable for fostering a climate where children are not allowed to celebrate their own culture, a fundamental failure in how to handle multicultural societys. This alone (as a microcosm for bigger but similar problems) makes immigration not worth it for me.
But apart from cultural enrichment, people also make an economic argument for immigration. How much does housing cost though, for legal and illegal immigrants? How much for food and transportation? How much for education (learning english as a start)? How much for the additional strain the NHS? How much for additional policing and a higher crime rate in general (Sweden saw a staggering increase since taking on a staggering amount of migrants)? In Germany I heard that almost half the money for the unemployed goes to migrants now. If this veritable mountain of money would go to the native population (the source of all this money), perhaps people would feel more inclined to have kids.
But there are also things way harder to quantify in monetary terms. How much does it cost to go from a high trust society to a low trust one? How much for losing the vote for women? How much for losing free speech? How much for losing democracy to theocracy? Some might think these points to be extreme, but the majority of muslims in the UK want sharia law. And this is exactly what you would get with that.
But importing cheap foreign labour will at least really show the billionairs, right?
