See the Onion Futures Act, which banned trading of onion futures in 1958. A brief summary is: experts have been divided on the effect that onion futures tradin

See the Onion Futures Act, which banned trading of onion futures in 1958. A brief summary is: experts have been divided on the effect that onion futures trading has on the volatility of onion prices. To me it sounds like the effect of trading on volatility is relatively small. Beware though that this stance tends to piss off people with both left and right political views.