The problem with placing the blame on the homeowners is that the state stepped in and saved some of the parties in question from counterparty risk. Yes, you should not take out a mortgage that's too big. But if you default the bank should also take a loss for doing such a bad job in giving you a loan.
AIG provided hedges against these bad loans. That, obviously, was a bad business move and they went belly up. But the intermediate banks never felt this counterparty risk because AIG was bailed out by the state.
The moral hazard is that the banks made bad loans and when the homeowners defaulted made large amounts on the hedges (sometimes more than the original capital of the loan). That would never have been possible without the taxpayer bailout, hence the anger.
It's was a fantastic PR move by several banks to publicly parade when they had paid off the bailout loans. The truth seems to be that it was peanuts compared to the money that flowed out from AIG through the hedges made.