We'll never know how this newly liberated financial sector might have performed on a playing field designed by Adam Smith. That's because government interventions of all kinds, from the defense budget to farm supports, shaped the business environment. No subsidy would prove more fateful than the massive federal commitment to residential real estate -- from the mortgage interest tax deduction to Fannie Mae and Freddie Mac to the Federal Reserve's low interest rates under Mr. Greenspan. Unregulated derivatives known as credit-default swaps did accentuate the boom in mortgage-based investments, by allowing investors to transfer risk rather than setting aside cash reserves. But government helped make mortgages a purportedly sure thing in the first place. Home prices seemed to stand on a solid floor built by Washington.That sounds about right.