Economists claim that the European monetary union would work so much better if labor mobility were as high as the United States. For comparative political economists, who conceptualize welfare states as institutionally coherent regimes, low mobility proves that free movement of persons clashes with the “logic of closure” (Ferrera) on which European welfare states rest. This paper takes free movement of citizens within the United States as reference point to show how homogenous social security systems are, how contested the social right of free movement is and what role courts play in shaping them. The basis for differentiated regulation of free movement in the euro and the dollar area is that welfare states consist of varied social programs with specific access rights. They operate on principles of discrimination, rather than closure. Judicial interventions can clash with these principles but there is no irreconcilable difference of logics at work. At the same time, labor migration as an economic adjustment mechanism for entire regions is arguably overrated, both in its positive and its negative impact.