The problem with ethanol based fuel, for instance, is that it's main source for production is corn, which has many more impacts than one would think. Already, farmers are feeling the effects. For instance, farmers use corn to feed their cows, which produce milk. Well, in order to to feed their cows now, they need to spend a lot more money because corn is in such high demand. This obviously causes milk rates to raise, along with a plethora of other goods that are effected negatively by the production of ethanol.

This is the epitome of an economics questions, because the cause and effect reaches such a vast area of fields, that it's very difficult to make an arguement for one side when it negatively effects another. It's like the age old question of, would you sacrifice one life in return for a thousand? What if it was your mom (or someone you love)? 10 for 1000? etc...

It's a double edge, either way. Either you're a tree hugger and like fuel efficiency for environmental reasons, etc. or you are for the produce, dairy, etc. farmers of the world.