What's the difference between a futures market and a casino? Very little. Futures markets began with farmers needing to find buyers for their crops before harvest time. Partly to have an arrangement for the harvest (what do you do with tons of crops if you don't have a buyer lined up?) and partly to lock in a good price. Crop buyers found the futures market leveled out prices over the year. Used to be, crops were dirt cheap right after harvest, and got steadily more expensive as harvest time receded into the past. Companies making bread or corn flakes or what ever, liked the steadier and more predictable prices provided by the futures market. All well and good, commodities futures markets have real economic value.
Now let us consider futures markets in stocks, crude oil, and God knows what else. Neither stocks nor crude oil has a harvest time. Production stays steady year round. Price fluctuation is unpredictable. Lucky buyers like Southwest Airlines can save them themselves lots of money, Unlucky buyers loose their shirts. This is really gambling and serves no economic purpose. Money sunk into commodities speculation isn't available for real economic investment. The recent spike in oil prices had a lot to do with tipping the economy into Great Depression II. And the even more recent fall has bankrupted a whole bunch of speculators.
In a free market economy we cannot prohibit buying and selling, but we can tax the bejesus out of it. And we can forbid Federal y insured banks from speculating in, our lending to speculators in the commodities markets.