Look, there are reasons that females aren't allowed in male quarters: one, is safety, for both the male and the female. If there are no females in the male only areas, their won't be any inappropriate conduct around said female, she can't get raped and no male soldier can be accused of sexual harassment, rape, or attempted rape. Second, is security; no one really knows who this non-resident female is. She might lift someone's personal affects. In that regard, that's why no civilians are typically allowed in any living quarters, not even soldiers from other units for the most part. That's just basic barracks security.
Just because your brother's chain of command was to weak and unprofessional to keep strangers out of their soldiers's living quarters doesn't mean that it's the norm; far from it in fact. Had your brother been in my unit, your butt would have been hanging out in the day-room and if you, or your brother had a problem with that, you could carry your self off post and he would be counciled as to what unit policy is, means and how it's to executed.