According to an article in the Economist magazine: In 1958 American onion farmers, blaming speculators for the volatility of their crops' prices, lobbied a congressman from Michigan named Gerald Ford to ban trading in onion futures.
Supported by the president-to-be, they got their way. Onion futures have been prohibited ever since.
Is it likely that banning trading futures contracts in onions reduced the volatility in onion prices? Are onion farmers as a group better off because of the ban?