Please, assume that I'm 12 years old, and try to explain.
There are many people in the world who use technology, but are offended by even the slightest sexual material. They might not have reasons for it that you and I would agree with, but that's beside the point. The point is that they can get very loud and insistent and they might go on TV saying that "Apple distributes smut" and whatnot. Apple wants to avoid that kind of hassle. There are different ways to do that, but the easiest for Apple is to simply reject any content they think might cause them this kind of trouble.
Ergo anything that implies that normal people can be healthy and happy and want to have sex threatens this world-view.
Kama Sutra - not ok.
Killing people app[1] - ok.
???
I have no idea where this comes from, if it stems from some kind of deep rooted puritanical culture, but it's not exactly unique to Apple's app store.
Whether having an app that talks about positions is going to make a 13 year old (more?) sexually active is a completely different question, but compounding the two is nonsense.
