Contrary to Ottodesu’s comment, the facts are that your “reason” is completely incorrect. First of all, the main reason for the collapse IS from derivatives, but the act you refer to has nothing to do with it, and in fact its impact has been measured.It was the false (and unregulated) belief by banks that they could package and sell “bad debt,” which encouraged them to go and GET bad debt in order to resell it. Greed is universal. It needs no encouragement. And the reduction or avoidance of any sort of regulation of banks (thanks, Reagan, Bush, Clinton, and Bush) contributed even more to it.