There is absolutely no moral or ethical dilemma in "jingle-mail". These banks handed out huge no-money down loans like candy to people who bought way more house (and in some case multiple houses) than they could legitimately afford. Both parties were complicit in a transaction that should never have occurred. Now that the inevitable has occurred and the music has stopped, the only thing that matters is the letter of the law regarding the contract. If the bank proposed/agreed to a no-recourse loan, just walk away.

Morality aside, jingle-mail is also the healthiest solution from a market perspective. The faster banks are forced to take their lumps, move these foreclosures through the market, and return lending standards to their historical norms (e.g. 20% down), the sooner the housing market can return to normalcy.