Sexually transmitted HPV (human papilloma virus) infects around 60% of all women of child-bearing age in this country (and that includes married women who aren't having sex with anyone but their husbands). One type of HPV has been shown to be responsible for virtually all cases of cervical cancer. The impermeability of the vagina to viruses should be big news to all the women who've died of cervical cancer, or had to have radical surgery for it to save their lives.
Hint to haole: Get your science from science publications, not from religious publications.
Unfortunantly, no one else will notice, check, or care.
1) That percentage is ridiculously too high.
2) The monogamous couples, the husband is not being faithful. The virus does magically "float in" their bedroom window and jump on them.
3) You make a big deal about the impermeability issue (which I admit I'm skeptical about) but IGNORE the MAJOR truth that sperm does carry immune-supressive factors that are very damaging when deposited in the "wrong" place.
I hate to sound ignorant about my own body, but I see the cervix and the vagina as two separate body parts. I would think that their cellular make-up is somewhat different as when getting a pap smear, I think only the cells of the cervix are taken. If the vagina and cervix were "the same", then shouldn't we be getting vaginal cells smeared too? It seems apparent that the cervix, for some reason, is much more likely to generate cancerous cells than the vaginal wall.
Other than HPV and HIV, I cannot think of another viral infection which affects that area. In both cases, the point of weakness could be the cervix rather than the vaginal wall.