Well how do we know that any scale at all is right?
My lab has weights that get calibrated against a NIST standard annually. We use those weights to perform daily quality control that our scale is accurate (to +/- 0.01g). If the quality control fails then we recalibrate the scale.
This overlooks that 100% cotton jeans will break down when they are discarded (unlike polyester and nylon). A good pair of jeans can be mended and worn for many years instead of a new pair every year. Jeans can lead a very useful "after life" as insulation or be recycled into new fabric.
It also ignores the chemicals and energy required to turn beechwood and bamboo into wearable fabric.
I don't know what the solution is but natural fabrics aren't the enemy.