” If a person is considered responsible enough to be issued a lethal weapon with orders to kill enemies and be prepared to die himself, why isn’t he considered able to drink in moderation responsibly, such as a 21 year old adult is permitted?”
But a military recruit goes through several weeks of intense training, during which he is supervised 24 hours a day. Even in combat, soldiers at the lower ranks are always supervised by NCO’s or officers.
Drinking alcohol, on the other hand, can be done without any training or supervision.