As the OP, I should say that speculation can be harnessed to produce some social value. A publicly traded stock market is economically useful. Commodities markets, well run, smooth out price variation. Derivatives let people get rid of risk in their business. E.g., if you're a wheat farmer it's handy to be able to lock in a price for your wheat even before it's harvested. And if you're a bread maker, it's valuable to insulate yourself from market price swings.

That said, I believe the industry's total value to others could be produced at far, far less total cost than now. And a lot of those very smart, very motivated people could be out there actually creating value for others.