Sure, these entities would be overseen by a “strong regulator,” as the Mortgage Bankers Association asserts. But if the credit crisis demonstrated anything, it was how easily regulators can be co-opted by the enterprises they are supposed to oversee. And if the mission of these “new” guarantors includes affordable-housing goals, you can be sure that regulators will again be persuaded to let them take more risks in the name of meeting homeownership benchmarks.

Happily, the Treasury report helps identify these possibilities when it describes how the taxpayers came to own Fannie and Freddie, at a current cost of about $150 billion. For example, the report states that the “profit-maximizing structure” at Fannie Mae and Freddie Mac undermined the companies’ public mission, while their perceived government backing conferred unfair advantages. It is hard to see why the new entities recommended by the financial industry, especially when they are owned by banks, would not have these dangerous characteristics as well.

Lest we forget, Fannie Mae and Freddie Mac were simply supposed to support liquidity in the mortgage market, according to their charters. They did not require the companies to actually add cash to a world already awash in home-loan money. But because executives at both companies wanted the lush profitability that such financings provided, Fannie and Freddie wound up pouring more liquidity into a system that did not need it.

That is the lesson of the financial crisis, at least where Freddie and Fannie are involved. Taxpayers surely do not want to create new government-sponsored enterprises that may later fail. So why not work toward a system where the government is solely the home lender of last resort? That way, the private market could operate in good times; the government would step in only if the market froze up.

Friday’s report seems to be leading in this direction. But it supplies no road map to a government system that provides a catastrophic insurance program only for those times when the private market is not working.

Such a program could insure privately underwritten mortgage securities at a cost based on in-depth analyses of loans in these pools. Using actual loan files, program administrators could estimate both current and historical losses of mortgages in the pools and base the cost of the insurance on the securities’ true risks. Insurance fees should not, repeat not, be based on credit ratings.

To be sure, any honest discussion of a new deal in mortgage finance will probably conclude that home loans would become more expensive. But if people put down more money when they bought homes, the risks associated with their mortgages would, in theory, be lower. As a result, their mortgage costs would decline, reflecting those lower risks.