That is the thing there... I was under the impression that everyone in the military be able to don MOP gear and be trained and ready for this situation. Without a clean shave, you can't get a proper seal and in the event of an attack, you are screwed along with potentially costing others their lives too if they are relying on you. But it seems today's military values a beard more than the safety of its soldiers. And for anyone who tells me chemical weapons are no longer used or a threat, I point you to Syria and the potential for an attack domestically that could come at any time.
I just have the feeling that this ruling is not coming from the military but from higher up.
https://en.wikipedia.org/wiki/MOPP