During the Dot-com bubble days Greenspan should have raised margin requirements to 100%. The housing bubble was/is a repeat of the Dot-com bubble. Lots of spec buying fueled by crazy low interest rates. Only difference is that, at least in desirable places to live — like SD — the underlying asset probably won’t go to zero. (In Detroit it effectively has gone to zero.) But it doesn’t need to for lots of reckless people and their stupid bankers to get deservedly hammered.