I'm not sure why we're this lax about privacy. The mothers usually don't seem to mind. Maybe it's because they have much more important things on their mind, such as contractions and pushing and trying to get a creature the size of a small bowling ball out of their uterus. Let me assure people that it is in no way a planned effort by the men so they can voyeuristically view womens' private parts. Trust me, there is nothing sexy about the bottom of a woman in labor. When I used to work at a suburban hospital, we seemed a little more conscientious about keeping mother from public view. Maybe modesty is just not that big a deal in the inner city.
The exceptions, not surprisingly, are some of our Moslem mothers from Central and Western Asia. I went to a delivery of one of them recently only to be greeted by an older woman related to the delivering mother, perhaps her mother or aunt, waving her hands at me and saying "No man, no man!" I managed to hide behind the curtain until the baby was delivered and we were sure he was fine. Sometimes not even the father is present at their deliveries.
I suppose we should pay more attention to this and do better, but until the mothers start complaining themselves, that's not likely to happen.