Robert Gordon on the state of macro-economics.

Perhaps the most glaring failure, thus far little discussed in the commentary on the financial meltdown, was the absence of Federal regulation requiring stringent downpayment requirements on residential mortgages. This is particularly ironic because the Fed's Regulations T, U, and X have long regulated margin requirements for stock market credit. Low 10 percent margin requirements were a culprit in the 1929 stock market bubble and crash (in contrast with 50 percent margin requirements on equities today), and the absence of tight regulations on residential mortgage down payments played a parallel role in the 2003-06 housing bubble and crash.
-- Robert Gordon

Of course, with enough inducement, even banks will be willing to stray into areas that don't agree with the spirit of the law....