The real culprit is Human greed.

In apportioning responsibility for the worldwide-credit crisis, readers did not all point to former U.S. Federal Reserve chairman Alan Greenspan. One called blaming Greenspan "simplistic," and another argued "banks were culpable." But after all is said and done, one wrote, "the real culprit is human greed."

http://www.newsweek.com/id/172636