That someone can make money on a downward trend, implying actual wealth is being lost, means money is being taken from someone else who knows less. It's just begging for those with advance information to legally rip off others, like Goldman Sachs did. In a ultra-competitive industry like banking, it's inevitable banks will legally abuse mechanisms as much as they can.

That is, if a mechanism can potentially be abused to rip off others financial institutions and destabilize the system with it, it [b]will[/b] destabilize the system. Therefore, the mechanism must be eliminated. This won't stop abuses but it will lessen the damage. All for the loss of the idea that you can make money from a company that is failing, not growing.