Of course, it doesn't really work that way. And that's part of the problem with green design.
Make a light bulb that uses less energy? Done: but now we have to deal with toxic cleanup issues, questions about mercury, and questions of taste over the color of the light.
Replace a hard-to-recycle plastic bag with one that can be recycled or reused? Done (again and again and again.) But we're constantly forgetting them or leaving them in the car -- and our beloved, carbon-spewing car is a much greater threat to the environment than even a lifetime of plastic bags.
The issue seems to be that, as human beings and as designers, we are really good at making and using stuff. What's not so easy for us to change is our patterns of behavior. We see the future of design lying in the design of products and services that, rather than making life "easier" by increasing the amount of stuff we buy and toss, instead present little challenges here and there that, through surprise and delight, encourage us to change our behavior.
A good example is Clay Moulton's Gravia lamp, which shows how little human energy it takes to get a lot of light and makes a virtue out of age.
image by macsony via sxc.hu