But that's not really what happened. Banks made a lot of poor quality loans, then packaged them up and sold them on, taking a spread in the process. Some banks (e.g. Bear Stearns and Lehman) kept some of that risk on their books, but others (Goldman) didn't.

This wasn't a case of banks using their mortgage book as collateral, it was banks originating and actively marketing a dangerous product. It's also worth noting that some banks knew that the products they were selling were low-quality and likely to default.

Then the US government stepped in and propped up the instigators of the crisis. People who made poor borrowing decisions had a part to play in the crisis too, but I think it's fair to argue that the pain could have been distributed more evenly.

Under the circumstances, I can see why it might seem fair to walk away from an obligation like the author's mortgage.