I think their are basically two types of mortgages in jeopardy of being defaulted - 1) those sold to people wanting to buy a house for the first time and being sold on their ability to pay. No matter their level of intelligence, they were deceived. The people selling the mortgages were raking in a commission on every mortgage and just wanted the sale. They deluded many of these people into thinking they could afford to buy. 2) flippers that were just in it for the money, sort of like us traders, they knew the risk of the trade. They probably already owned a home.
Any direct help to the homeowners should be directed to the first group - they could probably pay their initial loans unless they were "option ARMS", a real scam allowing you to pay whatever you wished and just have the missed payoff portion added on to the loan. Sort of like a credit card, but worse. The flippers should get the same help we get when we have a losing trade.
When the Wall Street firms packaged the mortgages they were able to sell the mortgages for more than they were worth. That is, by splitting the mortgages into payoff priority and interest steps, they could sell the split-out mortgage packages for about 20% more than the face value of all the mortgages. Thus, even paying off the mortgages leaves 20% of the entire sub-prime money problem as a loss to be absorbed by the package buyers.
The derivative side bets are a whole nother story.
Jack