It's all the fault of greedy Wall Street types

and everyone else is pure:

...Fannie, a government-sponsored company, had long helped Americans get cheaper home loans by serving as a powerful middleman, buying mortgages from lenders and banks and then holding or reselling them to Wall Street investors...

...Competitors were snatching lucrative parts of its business. *Congress was demanding that Mr. Mudd help steer more loans to low-income borrowers. Lenders were threatening to sell directly to Wall Street unless Fannie bought a bigger chunk of their riskiest loans...

...Disregarding warnings from his managers that lenders were making too many loans that would never be repaid, he steered Fannie into more treacherous corners of the mortgage market...NYT

Naturally Congress did not say how to do it; just to do it.

Added 3:30pm: The appetite for toxic mortgages was fueled by Fannie Mae and Freddie Mac, the super-regulated housing finance companies. [Columbia University's Charles Calomiris] calculates that Fannie and Freddie bought more than a third of the $3 trillion in junk mortgages created during the bubble and that they did so because heavy government oversight obliged them to push money toward marginal home purchasers*. Washington Post (opinion).

(And never spill coffee on your laptop keyboard. It sorta impairs typing.)

7 Oct: *Politics has fully entered now as Rep. Barney Frank calls these claims "racist."