Why are girls forbidden from seeing a ?

As an example, why are mothers overly protective of their daughter seeing a ? First, let me say, I know it is highly inappropriate for anyone to show a child a private part, that is not what I am asking here. I am asking why is the so stigmatized like this? I have been searching this question from a psychological/child development/parenting/sociological point of view, but cannot find anything that really addresses this issue. For a girl, as a child, a mother may shield a child (even physically by covering the eyes) from seeing a , may forbid a girl from entering a room or area where there may be an exposed , or even the complaints to the MPAA that now requires movie ratings to specify if there is "male nudity?" (and not specifying female nudity) The only thing I have been able to find on this is parents asking how to explain to their daughter what a is, which has had answers such as "explain that boys and girls are different" etc, though that does not really even touch the issue here, I think it is important to ask why this topic is extremely denied and not discussed in a logical way. It is as if mothers are afraid of their daughters being ually scarred by something that does not have to be addressed in a ual manner at all, but more from the approach of "the penis is used to pee, just as the is." It seems like this causes confusion for girls from the start, curiousity about the penis that is not addressed until an intimate situation that could have been better prepared for, and maybe a sense of inadequacy as a female, especially since boys are almost encouraged to be curious about females. I hope I'm getting my question across clearly, but mainly, I'm trying to point out the differences that occur between raising a boy vs raising a girl and that these issues are not so taboo when it comes to boys seeing a woman's or her , but when it comes to little girls, it is as if their "innocence" will be lost at the first sight of a penis. Why do you think this is so and what do you think about this from a non-gender bias standpoint? Your opinion is welcome, but facts and sources are encouraged.