Not to totally dismiss what happened on Wall Street, but when banks start lending to people who have horrible credit, they don't want those mortgages on the books. No one wants to buy one subprime mortgage, so you pool them up and diversify them, thinking that this will mitigate some of the risk. This would have worked had you not had the entire thing collapse. Taking out default insurance would of helped, except when everything failed at once.
A lot like the Titanic. The people who designed it said it was unsinkable, and it was, in 99.9% of circumstances. Unfortunately the .1% happened and they were proven horribly wrong.
Also, who exactly is going to be sent to the prison colony? This idea that there was one person, who master minded this entire fiasco ignores that there were many people involved, not just bankers. The government officials who encouraged this because home ownership is akin to apple pie in the USA, the bankers who raked in the fees and profits, as well as the people who bought more home than they knew they could afford or who used their house as a credit card to fuel consumer spending. All played a part and all share the blame.
Pointing the finger at Wall Street is a cop out and prevents people from shouldering their rightful portion of blame and thereby learning from their mistake.Just like buying stolen property and then crying when the police take it. You knew it was wrong, but instead of owning up to it, you blame the cops and the criminal.