Great idea.

So now the problem is that you have to write a detailed rule. A rule that allows for all legitimate cases of hedging and market-making will probably also open up large loopholes for proprietary trading. A rule that genuinely extirpates proprietary trading will probably trample on various instances of real hedging and market making. Life is complicated, and you often have to choose between overreach and loopholes when writing rules. And initially regulatory agencies seemed to be very much tilting toward writing a version of the rule that left plenty of loopholes in place. But there's been a late-game rally by advocates of a tougher version of the rule that's delaying finalization. Bart Chilton of the Commodities Futures Trading Commission says there are too many loopholes, and Kara Stein the new Democratic member of the Securities and Exchange Commission seems to have similar concerns.