If you want to get learn more about how the current mortgage crisis came about, This American Life recently did a great broadcast on it. They dissected the situation all the way from the person who had no business getting a mortgage to the person who had no business making that loan to the person who had no business buying that loan, and on up the chain of money.
The coverage has a nice balance. They don't vilify anyone as evil. But they don't excuse anyone from blame either. At each step of the way it's average people made bad decisions based on greed and peer/societal pressure.
You can listen to "The Giant Pool of Money" here. Or you can probably download it through iTunes.