They are not thinking about the electricity needed to weave the cotton into fabric or to cut and sew the fabric into a shirt. They are not thinking of the diesel fuel used by the cargo ship that brought it from Bangladesh and the truck that delivered it to the mall. All of these energy inputs are hidden from the consumer in the material economy. That is why we so often dispose of a cotton shirt so readily after it is snagged or gets a small stain. If we really understood the inputs all along the way and how they effected the environment, we would dispose of things less readily.
The other major problem with the material economy is the fact that it is an open system, not a closed system. Raw materials start at one end and waste products exit at the other end. This type of linear system sooner or later will run out of the raw materials needed to keep the system going. In a word, it is unsustainable in the long run. The system must be modified by changing it from a linear to a circular system of usage instead of consumption. This will ensure that the raw materials are not depleted at the extraction end. It will be replaced by recycling after usage. Disposal will be eliminated.