I agree, but take it one step further: it is unethical NOT to walk away. The whole point of the clause is to ensure everyone is taking equal risk in evaluating

I agree, but take it one step further: it is unethical NOT to walk away. The whole point of the clause is to ensure everyone is taking equal risk in evaluating the property: the bank and the owner. It is bad for banks to make loans without suitable collateral. It is bad for you to take loans you can't afford. In an overheated housing market, the house is NOT good collateral. The banks made a well-researched business decision to give you the mortgage with the house as collateral. They made a mistake (as did you) and everyone loses. The bank gets killed on the mortgage and you get killed on your original equity, interest and credit rating. It would be unethical not to walk away as this would encourage everyone to repeat the bad behavior.