Note this from Alan Greenspan's remarks to Congress today:

What went wrong with global economic policies that had worked so effectively for nearly four decades? The breakdown has been most apparent in the securitization of home mortgages. The evidence strongly suggests that without the excess demand from securitizers, subprime mortgage originations (undeniably the original source of crisis) would have been far smaller and defaults accordingly far fewer. But subprime mortgages pooled and sold as securities became subject to explosive demand from investors around the world. These mortgage backed securities being "subprime" were originally offered at what appeared to be exceptionally high risk-adjusted market interest rates. But with U.S. home prices still rising, delinquency and foreclosure rates were deceptively modest. Losses were minimal. To the most sophisticated investors in the world, they were wrongly viewed as a "steal."

The consequent surge in global demand for U.S. subprime securities by banks, hedge, and pension funds supported by unrealistically positive rating designations by credit agencies was, in my judgment, the core of the problem. Demand became so aggressive that too many securitizers and lenders believed they were able to create and sell mortgage backed securities so quickly that they never put their shareholders' capital at risk and hence did not have the incentive to evaluate the credit quality of what they were selling. Pressures on lenders to supply more "paper" collapsed subprime underwriting standards from 2005 forward. Uncritical acceptance of credit ratings by purchasers of these toxic assets has led to huge losses.

http://blogs.wsj.com/economics/2008/10/23/greenspan-testimony-on-sources-of-financial-crisis

What's notable here is that Greenspan says it was investor demand, NOT lenders and Fannie and Freddie being forced to make loans to the poor and minorities.  Another canard from the wingnuts shot down.