Interesting how there are hardly any non-medical terms for the vagina that aren't considered obscene or pornographic.
But why are they considered that way? Is it because the terms themselves are more obscene, or is it because we think about them differently because of the gender?
Why is calling a penis a weiner considered less obscene than calling a vulva a hairy clam? They're both crude descriptions of what genitalia look like by way of comparing their appearance to that of something more commonly seen. I'll admit that I don't have the biggest genital lexicography, but of the slang words I know for the female reproductive system, I don't see how the words themselves are inherently that much different from the male equivalents. Even a completely innocuous term like "va-jay-jay," which is derived directly from the medical term, tends to have a different reaction than an exactly equivalent term like "peen." It's the social context of the words. A term that describes female genitalia -- particularly the appearance of them -- is considered more obscene/pornographic/disrespectful than a term describing male genitalia with equal detail, because you're not supposed to know what female genitalia look like. You're not supposed to talk about them. Women are supposed to be paragons of modesty and poise and properness, and so removing their fig leaf is a much worse crime than removing mens'. (There's also an assumption of lack of female agency in there -- the one doing the removing of the fig leaf is presumed to be a man, and the possibility of a woman speaking like that is not considered (or, alternatively, she is considered a dangerous harlot).)
Same reason why when you hear about a 40-year-old male teacher having sex with a 15-year-old female student, your reaction is a lot different than when it's a 40-year-old female teacher having sex with a 15-year-old male student. Same reason why male victims of rape and domestic abuse are ignored or mocked, when there's about as many of them as there are female victims (way more if you include prison rape). Same reason there's so much more funding for breast cancer than for prostate cancer, which is just as big a killer. Gender roles. Women need to be protected and coddled and sheltered by their big strong men. Men aren't allowed to be weak. Women aren't allowed to be strong. It cuts both ways.
(Also, cancerous breasts are
so much sexier than cancerous prostates.)
It has roots in the sexual economy, where, due to human biology and evolutionary history, men are the consumers of sex and women are the suppliers. This can play out with either gender being in charge -- the women can be treated as commodities in and of themselves, with the men taking all they can carry; or the women can be acting as industries, making sure they are selling their goods to the highest bidders. This is one way in which feminism has unwittingly perpetuated the patriarchy -- whether the sexual economy is being dominated by men or by women, it's still an unequal and highly limiting system.
If you only try to free one gender from their gender roles, the overarching system will stay in place.