Well, real answer is first it was religious purity, then it was "THINK OF THE CHILDREN! THEY CAN'T BE ALLOWED TO KNOW ABOUT HUMAN ANATOMY!", and then it was "THINK OF THE WOMEN! THEY CAN'T BE ALLOWED TO KNOW THAT OTHER WOMEN HAVE ANATOMY THAT SOME MEN MIGHT FIND MORE ATTRACTIVE!"

This said by a man who prefers small/no breasts.