scaredycat, your example of the doctor in la earning $100K who could make $300K if he moved elsewhere is actually a good counterargument to the notion that walking away from debt should be easy.
If the person can earn more elsewhere, then they can pay their debts if they move. So they should move, and use the increase in their income to pay off the debt. Everything is working efficiently.
If the person were allowed to repudiate their debt without moving, they may not make the move, and they’d be earning $100K instead of $300K, and society as a whole would be worse off economically.
