Actually, the law used to be that active duty military personnel could purchase alcohol on military bases. In the early-mid 80s, MADD lobbied to have that amended so that the relevant state drinking laws would be in effect: TITLE 10 , Subtitle A , PART IV , CHAPTER 159 , Sec. 2683. So, your concerns have been addressed in the past, but I guess the feeling was that the lives that would be presumably saved by further curtailing "underaged" drinking outweighed the moral "rightness" of being old enough to drink if you're old enough to die for your country.