I just read an article comparing penetration of the vagina to the anus, and it is pretty enlightening, since it shows the anus as being MUCH more fragile to penetration ("i.e. one way street")
i can see why women would want to never take part in it, especially after reading this:
"The rectum is significantly different from the vagina with regard to suitability for penetration by a penis. The vagina has natural lubricants and is supported by a network of muscles. It is composed of a mucus membrane with a multi-layer stratified squamous epithelium that allows it to endure friction without damage and to resist the immunological actions caused by semen and sperm. In comparison, the anus is a delicate mechanism of small muscles that comprise an "exit-only" passage. With repeated trauma, friction and stretching, the sphincter loses its tone and its ability to maintain a tight seal. Consequently, anal intercourse leads to leakage of fecal material that can easily become chronic.
The potential for injury is exacerbated by the fact that the intestine has only a single layer of cells separating it from highly vascular tissue, that is, blood. Therefore, any organisms that are introduced into the rectum have a much easier time establishing a foothold for infection than they would in a vagina. The single layer tissue cannot withstand the friction associated with penile penetration, resulting in traumas that expose both participants to blood, organisms in feces, and a mixing of bodily fluids. Furthermore, ejaculate has components that are immunosuppressive. In the course of ordinary reproductive physiology, this allows the sperm to evade the immune defenses of the female. Rectal insemination of rabbits has shown that sperm impaired the immune defenses of the recipient.23 Semen may have a similar impact on humans.24 "
Pretty scary for the recipitent i would think;;; lol
There is no comparing anal and vaginal sex!
Heterosexual intercourse involving the vagina is less risky, in terms of tissue damage mainly due to lubrication. Heterosexual anal, is often an infrequent activity, done spur of the moment, with little preparation and therefore may lead to damage/contact with feces.
In contrast, homosexual male anal, no vaginas there
, involves individuals that "specialize" in preparation (kegels, lube, dilation, irrigation (reduces, some claim eliminates, fecal matter in the rectum), relaxation techniques, etc.) and training to bottom. Now, not all gay or bi men engage in anal sex, however, of those that do, most are experienced in reducing the risk of damage to their bodies.
As a heterosexual woman, I love anal, and was taught how to do it without pain or creating anal fissures. (
http://www.lpsg.org/85746-anal-sex-how.html) It is not an all the time thing, but when I desire anal I prepare appropriately, as I do for vaginal, and have not experienced any damage.
Regarding disease, bacteria, and fluid transmission, it is my opinion that anal, and vaginal sex (as it can also involve blood, mixing fluids, and tears), should always involve condoms.
However, I have never heard of immunosuppression due to anal, so I wonder if this is first, a fact, and also a significant risk or not. As Jason mentioned, please do cite your source as I would love to read the material.