(The thread on the same topic in the other forum was closed so I will reproduce one of my longer posts here)
I have not read Christopher West’s books or studied the “Theology of the Body” teachings of JPII so I cannot comment on Christopher West’s opinions. However, based on St. Thomas and St. Alphonsus, we have some principles we can work with. (I hope I am not being too obtuse in attempting to maintain some sense of modesty in mixed company.)
The purpose of the marital act is reproduction. Male genitals were made for female genitals, female genitals were made for male genitals. With regards to oral sex, it can be utilized in order to provide the needed stimulation to make the marital act possible if certain principles are followed. One of these principles is distinguishing between what is passive and what is active. When discussing a moral act, there is always the person who acts (active) and the person or object that is acted upon (passive). In the marital act, the nature of the act is such that the male is active and the female is passive (regardless of who is being more aggressive). It is the male organ that acts upon the female organ (‘vas’), not vice versa.
It is immoral to substitute another body part or object for either the male organ or the female organ. So thus oral stimulation on the man is morally licit as long as the mouth does not take the place of female organ. That is to say, as long as the woman takes the active role in this rather than a passive one. The same goes for the other direction, the man can orally stimulate the woman but again neither body parts nor foreign objects can morally substitute for the male organ. That is to say that all stimulation done by anything apart from the male organ must be done externally and not substitute for the male organ by penetration.
So when we discuss the issue of the posterior, how can it be licit? Here the backside is substituted for the ‘vas’ without a doubt, even if there is no pollution and hence it is immoral. However, It may be licit (again, I am not a moral theologian and I have not seen this discussed) to utilize other body parts or even foreign objects to stimulate that region since the genitals do not factor into it. But it still seems to be unnatural and disordered, akin to a fetish (a true fetish is where the erotic stimulation normally provided by the opposite sex is replaced by some other object – such as feet or women’s stockings) and so it should be ignored for the sake of modesty even though a small minority of individuals seem to have a proclivity towards anal stimulation. God gave us reproductive organs and that’s not one of them.
I was then asked for more specifics on where from St. Thomas and St. Alphonsus. St. Thomas:
St. Alphonsus treats of the issue in
Theologia Moralis, Bk. IV, Tract. IV, Sect. 466. St. Alphonsus treats explicitly of these issues but it is in Latin so it softens it somewhat.
Fr. Chad Ripperger, FSSP, formerly professor of dogmatic and moral theology at the FSSP seminary in the United States and a solid Thomist gives a candid overview of the issues during a series of talks on marriage (this was to an audience of men). He tries to balance speaking frankly and speaking modestly about the issues but errors on the side of frankness.
Here is the sermon (44min).