An important factor for me, not mentioned in your poll, is energy conservation. Although related to the answer on environmental reasons, it goes beyond that. We waste so much gasoline, diesel and other fuels in the US and supplies are ultimately limited. One day we will run out, or gasoline will be too expensive for most people to buy. Our addiction to petroleum also drives much of our foreign policy, causing us to get involved in stupid wars and conflicts that would otherwise be unnecessary.