like other professions and other markets it all depends on whether the entrepreneur profits. if he profits than it helps society if he takes loses than it harms society. If he profits than he reduces volatility, if he takes losses than he increases volatility. this is because if he profits than he succeeds in buying the tops, thus reducing the exaggeration of the top and if he sells the bottom than he reduces the exaggeration of the bottom.

if you have a mind for seeing abstract connections between seemingly disparate ideas, than in this video bob murphy explains the same idea in abstract except with a different example. see if you can make the connections http://www.youtube.com/watch?v=VKk3vCbnigc