I haven't looked into how much of the mortgage mess is due to financial institutions giving mortgages to low-wage workers, including illegal aliens from Mexico; for that, see Steve Sailer. Some but not all of it was, making the June 10, 2004 article from The Economist called "More Mexicans, please" (no author given; economist.com/world/unitedstates/displaystory.cfm?story_id=2752598) a cautionary tale about a) giving in to corruption, and b) trusting The Economist:

NATIVISTS in Texas and Arizona may still want to keep Mexicans out of America, but in the mid-west, far from the border, a growing chorus is calling for better integration of the large Mexican population that already exists. Employers need them, schools are full of their children, politicians seek their votes and, increasingly, banks want their money.

The integration push is already under way at the Mexican consulate in Chicago. Under a programme set up this spring by the Institute for Mexicans Abroad (a government agency created by Mr Fox), daily lectures are held there on topics ranging from worker rights to banking and health care. From 7am each day, crowds of people line up to apply for an identity card known as a matricula consular, which is now accepted as valid ID by 800 law-enforcement agencies across America. As the matriculas have gained wider acceptance, doors have opened to immigrants in other areas, blurring the line between services available to legal and illegal Mexicans.

Now financial institutions are courting these hard-working people. No wonder: Mexicans sent $13.3 billion in remittances home from America last year (providing the second-largest source of income after oil), and three-quarters of those who remit funds have no bank accounts. A growing number of banks (118 nationwide, including 86 in the mid-west) now accept alternative forms of identification—generally the matricula card along with a taxpayer identification number—to open bank accounts. Thirty-three of the 48 American banks that offer international remittance services are in the mid-west, and America's bank regulators are encouraging the efforts. “Banks aren't so interested in the remittances, they're interested in the relationships,” says Michael Frias, an official with the Federal Deposit Insurance Corporation (FDIC). “They're looking at this as a long-term proposition.”

Indeed, and we'll be paying for the decisions made by the FDIC and those like them for a while. For more on this from around the same time as the Economist article, see this, this, this, and more recent examples of this type of corruption are listed on the immigration banks page.