I believe that when you enter into a financial agreement, you have an obligation to pay that debt. That is how I was raised.

However, I would not fault anyone from walking away from a severely depressed property. The banks knew that they were writing loans that were going to head south. Some (Goldman Sachs) even shorted those same loan products at the same time they were writing them. By doing so, they doomed the real estate industry to its eventual fate, not just the sub-prime borrowers that were unlikely to meet these loan obligations.

When enter into an agreement with a dishonest or fraudulent entity, the entire equation changes, IMO.