Your prerequisite doesn't follow through to your (apparent?) conclusion; there's no logical connection I can see. Let's say opening borders does have to to be

Your prerequisite doesn't follow through to your (apparent?) conclusion; there's no logical connection I can see. Let's say opening borders does have to to be accompanied by economic development: fine. How does that then not work when migration occurs from areas with different economic situations? You seem to be proposing that migrants from economically areas necessarily depress a developed economy?