In the fall of 2008, America's wealthiest companies were in a pickle. Short-selling hedge funds, smelling blood as the global economy cratered, loaded up with bets against finance stocks, pouring downward pressure on teetering, hyper-leveraged firms like Morgan Stanley and Citigroup. The free-market purists at the banks begged the government to stop the music, and when the S.E.C. complied with a ban on financial short sales, conventional wisdom let out a cheer.

"This will absolutely make a difference," economist Peter Cardillo told CNN. "Now, if there is any good news, shorts will have to cover."

At the time, poor beleaguered banks were victims, while hedge funds betting them down as the economy circled the drain were seen as antisocial monsters. "They are like looters after a hurricane," seethed Andrew Cuomo, then-Attorney General of New York State, who "promised to intensify investigations into short selling abuses.