The end of the federal 45-cent-per-gallon tax credit for U.S. oil companies that buy and blend ethanol with gasoline has boosted pump prices by a nickel, but largely drowned out by consumers' grumbling were two valuable civics lessons. The feds require fuel blends that are 10 percent ethanol for most vehicles, and going forward, they have guaranteed greater demand for ethanol with their escalating alternative-fuel mandate. Adopted in the 1980s and twinned with a 54-cent-per-gallon tariff on imported ethanol, the tax credit transformed grain markets by encouraging farmers to devote more acres to corn. That reduced the production of other...