The lassie fare regulation of the "shadow banking" sector cannot be attributed to be the entire cause of the GFC. After the 01 reccession, the FED was reluctant to raise the domestic interest rate, to slow down growth and thus sacrifice jobs. With the i < i (n), this led to output being above the natural level, as consumption was prosperous.
There was also severe and growing financial imbalances since the AFC in 97 which combined with the share market boom eventually lead to the housing buble burst.