The energy required to power a laser that can melt a man is enormous. How long could a town like Shady Sands run on what it takes to fire one lousy round with a plasma rifle? A month? longer? Yet no one can manage to build simple vehicles that use this power? Or factories? Someone needs to figure out how to put those miraculous little power cells to work. If you have such a potent sourse of power, there is nothing you couldn't do. Thus, ray guns in the post apocalypse = facepalm.