When millions of homeowners defaulted on their mortgages in 2008, many pointed the finger at two less obvious culprits: Fannie Mae and Freddie Mac. The two mega mortgage buyers had been picking up risky loans and selling them with a guarantee of repayment. This amplified the housing crisis and forced the Federal government to bail them out. Ever since, there's been a serious movement to dismantle Fannie and Freddie. But last week, Chicago Harris Professor Benjamin Keys released a paper suggesting that Fannie and Freddie might be doing the economy a hidden favor by redistributing risk and cash - to the tune of $20 billion.