The question of immigration needs to be taken away from the right…and the left. I am not sure I understand the issue in European terms, but sooner or later the left itself has to propose a better solution: modern nation states should welcome immigrants, be willing to give a percentage portion of their GDP, but beyond a certain point immigration will sink modernity. It might, would put it better.
The alternate better solution is to examine the conditions of the source cultures, and bring them into modernity. Too often they have instead been sunk by imperialism, capitalist globalization, the list continues. Immigration seems to spring from multiple motives: one of them a sort of ‘refund’ for paying the cost of modernity in capitalist injustice and getting none of the benefits. The issue is clear: economic globalization isn’t really modernization.
One thing that would equalize would be for Western ‘immigrants’ to find a place in the source cultures. That can actually backfire, but in principle it is a useful concept.