After all, understanding the environmental implications of something as simple as paper versus plastic shopping bags requires digesting a fair amount of science, some of which is inconclusive, contradictory, or simply arguable. Both, after all, come from limited, declining resources, can be made from recycled material, and can be recycled. Even the scientists don't agree. Never mind the slightly more weighty consumer choices. Like which kind of car to buy, or whether one even needs to own a car.
Old myths die hard.
People lack perspective. Similarly, most people don't have a clue about the relative environmental impacts of the things they do every day. You make the call. The whole notion of green consumerism itself unwittingly contributes to this lack of perspective. The dirty little secret of green consumerism is that we're not likely to shop our way to environmental health.