There is nothing immoral about ditching your mortgage.

A solid two years into the housing bust, the national foreclosure wave doesn't show the least signs of abating. Banks that had called a foreclosure moratorium are now back to the business of taking back properties, and the foreclosure numbers are again at record highs. As the foreclosures rise, so too does the criticism of “walkaways” who hand the keys to their drastically devalued houses back to the bank.

Last month a study from the credit reporting agency Experian and consulting outfit Oliver Wyman estimated that close to a fifth of troubled mortgages involved borrowers who were “strategically” defaulting—walking away from mortgages they could pay but decided not to because they owed more than their houses were worth. Self-assigned guardians of financial ethics see the willingness of borrowers to abandon their mortgage debts as a sign of the “erosion of social and moral standards.” The aim of these critics is to shame debtors into sticking with their mortgages. That's something debtors should take with a grain of salt. There are many good reasons to keep paying your mortgage and avoid the black mark of foreclosure, but the immorality of sticking the bank with a loss isn't one of them.

Some observers, like Zubin Jelveh of the New Republic, have taken issue with the Experian-Wyman study's methods, arguing that it was too broad in defining “strategic” default. But unlike some other reports that play up the number of deadbeat debtors, this study uses a fairly narrow and defensible definition to arrive at its conclusion that 18 percent of mortgage defaults are “strategic.” (Experian showed the report to The Big Money, but asked that it not be posted.) The study focuses on borrowers who, once they hit 60 days late, roll straight through to foreclosure without ever making another payment and manage to stay current on all their credit cards.

These are pretty good signs that someone could try harder to pay the mortgage—an idea supported by the fact that the borrowers who fit the model often had higher credit scores (and so probably more financial knowledge) and tend to live in states such as California, in which banks can't keep pursuing them for more money after taking their houses.

So let's say the Experian/Wyman study is right in its assessment that there are a fair number of strategic defaulters. Those who use this study and others like it to argue that the foreclosure problem is one of moral failure among borrowers are still wrong. Borrowers who walk away from mortgages calculating that they're better off taking the risk of not paying aren't abusing the system. They're using it the way it's designed to be used.

“Strategic default” is generally seen as an issue arising from laws in some states—including California, the reeling giant of the housing bust—that make traditional mortgages “nonrecourse," meaning they don't allow lenders to pursue any shortfall after foreclosing on a house. This is a bit of a simplification, as the actual rules are complicated, especially if multiple mortgages or refinancing is involved. In California, for instance, mortgages that have been refinanced are technically no longer “nonrecourse.” They remain subject, however, to the state's “one-action rule,” which forces banks to choose between a relatively quick nonjudicial foreclosure and a much longer and more involved process of suing for all the money they're due.  As a practical matter, walking away from your mortgage is a more involved process than it might seem and not, as the critics sometimes imagine, simply a matter of living in a nonrecourse state.