This has always been my question to the people advocating no cars. First, the original energy and resources can't be undone (although certainly recycling does recover much of the material). The original extraction is done, might as well use the truck until most of the body is returned to the elements. Second, bikes, shoes, buses, trains, all forms of travel. Where you do suppose all that metal, rubber, synthetics and leather came from? They didn't just magically appear, they were mined or otherwise collected from somewhere.
I don't think it's possible to truly be an vehicle supported environmentalist, because in no way is it the lowest impact method. It is the most convenient, but walking or other human powered vehicle uses less resources. But instead of covering hundreds of miles in the weekend, you will covers tens of miles a day and the amount of stuff you can carry is limited. We can fool ourselves by saying we use less than the other guy or that diesel is less harmful, but it's still a pretty inefficient use of the resources. It is a more efficient use of our time and that's the point of doing it, but it's still relatively wasteful and self serving. It's a function of the society we have made, that we are driven to work, work, work, consume, consume, consume. That leaves limited time to travel and so it is what it is. We are victims of our own productivity. We all own computers, which are not absolutely necessary to survive. They make life better (or such is the presumption) and we trade the impact of making them has over the benefits we perceive from having one.
See about electronics and toxic chemicals:
http://www.computertakeback.com/the_...cchemicals.cfm