In addition to the engine damage problems caused by lean burn explained by Al, above, high combustion temperatures and an excess of oxygen cause the formation of oxides of nitrogen. The respiratory problems caused by air pollution are due in large part to these emissions and reducing them is an important goal of environmentally sensitive vehicles. The Honda Insight has special equipment to trap and convert oxides of nitrogen in the exhaust. Even so, with lean burn it is unable to qualify as a SULEV vehicle because of the remaining oxides of nitrogen that cannot be removed.
You realize that in the same sentence you admit that you have no idea what they’re growing over there, but you’re sure that they’re eliminating food crops for biofuels? How can that be? And even if that is the case, thats actually a GOOD thing. If farmers are paid MORE for their crop, they’ll grow MORE of it. That eventually leads to a surplus, which brings local prices down. That how farming in America got to where it is today. We were all subsistance farmers just 200 years ago, but we got better and made a surplus. That meant less people had to farm and food got cheaper. Today we’re the best in the world at it.