The bulbous root is the only commodity for which futures trading is banned. Back in 1958, onion growers convinced themselves that futures traders (and not the new farms sprouting up in Wisconsin) were responsible for falling onion prices, so they lobbied an up-and-coming Michigan Congressman named Gerald Ford to push through a law banning all futures trading in onions. The law still stands.

And yet even with no traders to blame, the volatility in onion prices makes the swings in oil and corn look tame, reinforcing academics' belief that futures trading diminishes extreme price swings.

...

Since 2006, oil prices have risen 100%, and corn is up 300%. But onion prices soared 400% between October 2006 and April 2007...

So do we really expect Congress to learn from history, or do we expect them to blame the speculators?