Galileo Blogs has a compact post on the value of market speculators. Lots of people seem to think that speculators are just irresponsible hustlers who do nothing but mindlessly gamble on whether some aspect of the market will go up or down. Nothing could be further from the truth.
In fact speculators actually help market downturns to correct sooner than they would if there were no speculators or if they were severely restricted by government regulations.
Walter Williams also has an article on the value of speculators at Capitalism Magazine.