The history of mankind is a history of migrations.
Be it for food, wealth, climate, wars or whatever.
I think building walls, creating a 'us vs them' culture is kinda shortsighted.
For sure it may have positive short-terms implications, from a strictly economic point of view.
But we are expanding so rapidly, and our influence on our habitat is so dramatic, that we should start to think more in perspective, and as a "whole".
OR, we could stop making children, realize we are fucked up anyway and walk hand in hand towards extinction, but that's a bit unpopular.