Thanks for the many links, fetal (and for following up by FreepMail). I’ve been away for the weekend.
I was not debating that anal sex can be dangerous (as can vaginal sex) when one of the parties has a sexually transmittable disorder. That’s pretty clear. I was particularly curious about the “disoriented sperm” claim — I hadn’t heard it before.
The article you linked from NARTH gave a rationale, and cited a 1977 study. I did a quick lit search on the topic. It seems that this claim is echoed only in a handful of religiously oriented sites (usually using the same “two-in-one-flesh” wording, so I think they’re probably loosely copied from one another, and all citing the same 1977 study). I can’t access the study (the journal is only online from 1998 forward), and I can’t find any mention of the same explanation for anal cancer anywhere else in the scientific literature or from any credible independent source (one that doesn’t use the same religious language).
We really don’t know what causes anal cancer, although exposure to HPV (which isn’t necessarily prevented with condoms) seems to be a strong marker for it, and smoking increases the risk. There’s a good summary on the matter from the American Cancer Society here:
It doesn’t have anything to say about disoriented sperm. I am starting to think that this may be a bit of an overblown hypothesis derived from that early study. Do you have any other leads on it?