I think factually what caused this situation is, Redlining. Banks had to lend to ARM's to high risk, high debt to income clients.
In other words - OVER REGULATION.
Not really. It has a lot more to do with investment banks taking those high-risk loans, bundling them together, and selling them as though they were low-risk investments. Lots of banks, insurance companies, pension funds, etc. invested in those surprisingly high-risk investments. Now, no one wants to buy these bundled loans.
That's your problem. You're trying to simplify a complex issue - and consequently missing the point.