At the end of the recently released film "Margin Call," the chairman of the fictional investment bank that triggered the mortgage-backed securities meltdown sits in his executive dining room, looking down on the Hudson River sunset while enjoying a steak and an expensive bottle of Bordeaux. Why not? He has just saved billions for his shareholders by dumping the firm's entire "toxic loan" portfolio in one hectic trading day. Just before giving a bonus to the brilliant analyst who foresaw the meltdown only hours in advance, the chairman predicts, "There's going to be a lot of money made coming out of this mess."

Wall Street understands how to make money, up-market or down. "Margin Call" may fuel Occupy movement ire, but in creating mortgage-backed securities, Wall Street did nothing other than facilitate home-financing access to the next tier of less-qualified home buyers, as demanded by every president since Bill Clinton. After that, the bankers did exactly what their shareholders wanted: bundle those risky loans into securities, sell them to lock in the profits, and dump the risk right back onto the federal government—where it belonged.

My purpose is not to debate the morality of mortgage-backed securities but to update the Law of Unintended Consequences with the corollary Law of Misguided Subsidies: Whenever Washington disrupts a market by dumping subsidies into it, Wall Street will find a way to pocket a majority of the money while the intended subsidy beneficiaries are harmed by the resulting market turmoil.

The recent crash in mortgage-backed securities was a near-repeat of the savings-and-loan crash of the 1980s, in which Washington insured the S&L industry but failed to set limits on high-risk loans. When the bubble burst, Washington paid Wall Street the insurance money while homeowners lost huge sums in real-estate hell. Wall Street understands how to manage risk; the federal government and consumers do not.

Consider the current 30% federal solar energy subsidy. A home solar system with 60 solar panels produces about 15,000 watts of power, enough to completely offset the $6,000 annual electricity bill of a typical upscale California home. The system costs about $90,000 prior to the 30% federal income-tax credit, which reduces its cost to $63,000. After a simple payback period of about 10 years, the homeowner literally enjoys free electricity for the remainder of the guaranteed 20-year system life, a very profitable 10 years.