Mort Zuckerman writes a helpful essay explaining the complex world of mortgage finance and the role of derivatives, and lays much of the blame for the crisis we are going through squarely where it belongs, on the Congress of the United States, instead of on Wall Street:
But we also need to understand how the housing market got as hot as it did. Why did it keep rising, generating more and more derivatives geared to a rising market? It turns out that Fannie Mae, Freddie Mac, and the Federal Housing Administration had financed a lot more subprime and Alt-A (alternative documentation) loans than anyone realized, mostly as a result of congressional mandates. Indeed, of their total outstanding mortgage portfolios of $10.6 trillion, roughly half turned out to be of low quality. Had this been known, it would have been clear that the American public's capacity to assume this amount of housing debt was at great risk.
That is at the heart of the now-famous Goldman-Paulson saga. Hedge fund manager John Paulson judged that the housing market was a bubble, so he shorted the securities through Goldman Sachs and an insurer called ACA, which sold the package to a German bank. The buyers judged that it was safe to count on housing prices continuing to rise. They chose which mortgage securities would be bundled by Goldman. And they have paid a heavy price for their judgment.
The American public has hereby had a peek into the bewildering complexities of the world of finance. The natural instinct is for the public to blame the housing decline on those who shorted. But it is the other way around. They should be blaming those who let the market get pumped up, inviting a dramatic and painful correction that took most people by surprise.
The complete story is well worth reading, here.