It's a pretty artificial thing. I've written about it and other taboos. Some places people run around topless all the time and people are used to it. Go far enough into the past and the big dresses and such and when a woman showed her ANKLE it was sexual exciting. Then go to places like the outback or tribes in Africa and south america and guys might only wear a Penis Sheathe.

Taboos occur the same way as laws. Someone decides people should behave in a certain way. If they have enough people backing them they make it enFORCEable.

We could do away with all of this censorship, and taboo concerns, but it'd likely require a serious awakening of the minds of the populace, and it might require some religions to go away, or seriously change.