Those who were and are involved in instances of fraud (robo-signers, brokers who mis-stated incomes/assets and appraisers who inflated values of homes, plus all those above them in the chain who specified that it should be done) should be prosecuted for fraud.

I'm not sure if there's a criminal case for breach of fiduciary duty at the federal level, but if there is, I wouldn't be adverse to seeing some trials for that.