Also, if you have ever been to Japan (in modern times, not 10,000 years ago when our civilization was like this), your 'hide private parts of woman from children' ideal will fall apart instantly. You would have to ban your child from going anywhere. Convenience stores, department stores, groceries, even walking down some streets (which sometimes have magazine vending machines). Japan has strict censorship laws which even covers manga. However, it covers manga no less than it covers actual porn. That's right. Those three tiny strikes going horizontally through the crotch of whatever sex your into is all that is drawn over the porn. Wait, I'm not finished. The page with the crotch is.... THE FRONT COVER! Wait, it gets better... Most stores place these magazines.... at the exit! That's right, you cant leave without seeing them! God, I miss Family Mart. Though I don't miss seeing guys peeing on the sides of buildings. That was gross.
That said, I was mostly messing with you. I am fully aware that common sense in manga is to cover the parts, partially because the target audience would change if they did not. I don't think that it would be common sense IRL. If your dog suddenly transformed into a loli, common sense would be to run for your life or go see a psychiatrist. If there is a group of 4 friends, and one of the girls suddenly stripped. Common sense would be for the other girl to leave, play with her, or strip as well (peer pressure you know?). This is coming from a guy destined to be a virgin for the rest of his life though, so take it with a grain of salt. Don't retort and break my fantasy here!