I agree with Aunthill. It´s largely a matter of control. They want to be different, not because what they shun is necessarily bad, but for the sake of being different. If everyone in the world decided short hair and no beards was cool, all JWs would have long hair and beards by the next convention. Controlling the smaller details of one´s life goes along with the larger scheme of controlling a JW´s mind.
Ron