Most people don't even know what that means, so I'll help out.
What Wall Street calls mortgage securities is what you call your home mortgage. Wall Street trades home mortgages like you trade stocks online.
Well, if the trading prices for those securities plunges, then someone is going to pay less for your home mortgage than what the bank gave to you to buy your house. A $150,000 home loan might be sold for $140,000.
Now, what America needs is a simple law that says that home owners get an email notification if their own home loan note is being offered for sale at less than face value.
Wouldn't it be cool if you could purchase your own mortgage back at a discount! The bank gave you $150k to buy your house. Then some banker who owned your $150k mortgage note got scared and sold it back to you at a firesale price (say, $100 grand). Talk about dropping your monthly payments!
But such a law would have another effect: it would add new buyers into the mortgage market. The potential for a large-scale shock to the system would forever be mitigated by the sheer numbers of new mortgage buyers on the secondary market.
You'd get access to reducing what you owed. The mortgage market would gain yet another safety net. Home values would be further shielded, too.