Did Fannie and Freddie really cause the housing bubble? Paul Krugman posted some interesting graphs that suggest the answer is "no." They show the percentage of mortgages securitized by Fannie Mae (NYSE: FNM) and Freddie Mac (NYSE: FRE) declining in the lead-up to the bubble's peak, while the share of private securitization by top CDO securitizers Merrill Lynch (now part of Bank of America (NYSE: BAC)), Citigroup (NYSE: C), Wachovia (now part of Wells Fargo (NYSE: WFC)), and Goldman Sachs (NYSE: GS) went through the roof.

This isn't to suggest that Fannie and Freddie were a paradigm of corporate governance, or that they don't badly need reform. But it does raise some questions about the widespread belief that the government-sponsored entities were the primary cause of the housing bubble and that if we just fix them everything will be hunky-dory.

Fool editor Ilan Moscovitz doesn't own shares of any company mentioned. The Motley Fool is investors writing for investors.