I have thought of what you 've said; though I haven't any idea what books you have read to support you assertion about anal sex being safe, I still insist on my view: anal sex is really prohibitive. understandable even by general layman without any medical expertise.
What is contained at the anus? It is faeces and excretion. you surely can't always be sure if your anus is clean but inserting your penis into that ass-hole, may leave some bit of the excreta inside the penis that may eventually cause infection. It may happen even though both of the couples are healthy. (unlike the situation when "normal" sex is going on with vagina)
In addition, there is no lubricant inside the anal canal; despite so, why is oral sex okay but not anal sex? It is simply because saliva is sterilizing but excretion inside the anal canal is not. You can't rely on your penis to sterilize, unlike the vaginal fluid and semen. that must protect the sperms from bacteria or reproduction is meaningless. Hey i am not a medical expert. But it is quite reasonable to think about it right? you don't need any medical expertise; you still can tell it must be so.
You can again imagine another situation if you eat with your nostril instead of your month, please tell me, Mr "Man very deprived", does it cause pleasure to you? I can't deny there can be some people who are into it very much. Even though I am just a layman, not a medical practitioner, I can tell it causes infection to your respirotary canal. It is just common senses.
I only take a glimpse over the web-pages about anal sex. Unlike masterbation, I didn't read them in details. It doesn't keep me from realizing that almost all web-page supports the pleasure of anal sex. May you be reminded, web-pages and articles published can be commercially oriented. It tries to please the surfers for more market share so advertising income may rise. If it finds out the market goes in favor of anal sex (in fact, anal sex pleases number of people), do you open a web-page or publish books against anal sex that you subject yourself to declining surfers' number and advertising income and sponsors? (I bet that's why you can't find a Christian-written books in favor of anal sex to convince your wife. For ethical reasons, most Christians may take the stance against anal sex; leaving alone this issue, they needn't face the economical dilmma and ethical remarks for and against their view that is of no benefit to them, in terms of fame and evangelism)
The situation is the same asin masterbation, most books and web-pages are opened in favor of it. I am quite against it, not because of biblical teachings (that i find some justification in other threads i posted), but because my experience assures me of the influence of masterbation to my healthy life ("more attentive" and "less dizziness" and "smarter performance" when I practised no masterbation for a month)
But masterbation is different from anal sex. Ethically, it is apparently okay for masterbation. It is quite natural use of sex. But anal sex is not. It is not hygienic.