Securitization was an attempt at managing risk. There have been a number of attempts to mitigate risk, or insure against problems. While these are legitimate things to do, the instruments that allowed this to happen helped cause the current problems, too.
In essence, what had happened was that banks, hedge funds and others had become over-confident as they all thought they had figured out how to take on risk and make money more effectively. As they initially made more money taking more risks, they reinforced their own view that they had...