Chemical warfare is a serious business.
Someone in the military spends the large majority of their career outside of combat zones. There is no drinking allowed when deployed, but that doesn’t mean everyone in the military has to be a teetotaler. There would be nothing wrong about telling people to shave before deploying or for field exercises.
I flew, and the oxygen mask would not be compatible with a beard. THAT I understood. But I never understood why the only legal mustache in the USAF was one like Hitler’s...