The government’s civil fraud case against Goldman Sachs raises so many provocative questions.

Did the firm deliberately mislead its clients who bought a mortgage-related investment without the knowledge that it was devised to fail? Was it fair that a bearish hedge fund manager helped to pick the parts of an investment marketed as bullish, so that he could bask in the winnings?

Who besides the vice president named in the lawsuit knew details of the deal in question? Were there other deals like this one?

But if there is a larger question, it is this: Why was Goldman, or any regulated bank, allowed to create and sell a product like the synthetic collateralized debt obligation at the center of this case? What purpose does a synthetic C.D.O., which contains no actual mortgage bonds, serve for the capital markets, and for society?

The blaring Goldman Sachs headlines of the last few days have given the public a crash course in synthetic C.D.O.’s. Many more people now know that synthetic C.D.O.’s are a simple wager.