> You're also negating that folks defaulting massively hinders their ability to move in the financial system.
Quite the contrary. Lenders will lend to you immediately after bankruptcy because you can't default again for seven years, for example. If you have bad credit, you can still get credit! Just at a higher interest rate. I am familiar with lenders who will get you a mortgage the day after foreclosure for 200-250 basis points over conventional rates (6-6.5% versus 4%, in this case).
Economic drag due to student loan debt that can't be discharged is a separate issue (with those debtors delaying or opting out entirely of home ownership and/or children). Pensions will get dumped onto the Pension Guarantee Corp with a reduced benefit payment to those entitled to such, and any federal debt will get inflated away through the Fed (not great, but what happens when you have your own central bank).
As I said, I think the only "great unwind" or credit crunch in the near future is corporate bonds.