His perversity goes way back. In one of the Dangerous Visions anthologies (either the second or the third) there is a short story called ‘In the Barn’. It’s about an explorer who is sent to an alternate Earth where all large mammals except man died out for some reason, and humans have started keeping other humans (who are kept stupid by being kept in sensory deprivation on a low-protein diet for the first two years of their life) as livestock.
OK, and interesting enough idea. The explorer has to investigate a barn to find out what they are using for animals, and it turns out it’s a dairy barn. His descriptions of naked women with enormous breasts kept in pens and milked by machines is not what bothered me - he’s trying to show some of the less savory aspects of ranching by putting humans in the role of the animals. But there is a scene where the guy has to take a young ‘cow’ which just reached breeding age to the bull for it’s first mating. When he’s alone in the pen with the retarded teenage girl the main character sees a resemblance between the girl and a bitchy domineering woman he has a crush on and decides to have sex with her himself. He actually penetrates her, but is unable to get off because she has extremely loose genitalia, supposedly because they were bred for easy birthing - the line was ‘He could not plumb her well to it’s depth, nor gain purchase at the rim’. Sexually frustrated he gives up and takes her to the bull (which is a big, hairy, very well-endowed man) and then there is a vividly described brutal sex scene, and the main character gets some kind of satisfaction out of seeing her get it.
The thing that bothered me the most about this sequence is that the main character isn’t just some random weirdo who happened to wander into this alternate universe, he’s supposedly a highly-trained explorer, like an astronaut the best-of-the-best. He’s supposed to be the representative of normalcy, the guy the readers sympathize with and see this world through. There is a bit of text devoted to his questioning whether or not he should screw the cow (with him rationalizing that she was going to get it anyway) but he doesn’t feel any guilt or seem to think that what he did was wrong, it didn’t matter because the girl was raised as an animal and was mentally inferior to himself (though I remember that he thought he saw a glimmmer of intelligence in her eyes at first). If you are going to make your main character do something morally abhorrent then you better give a better explanation why he’s fucked up like that, other than ‘She looked like this stuck-up bitch he had the hots for and couldn’t help himself’.
Come to think of it, I can’t think of anything I’ve read by Piers Anthony that didn’t have perverted elements in it. That alone doesn’t make me think the author’s sick, because healthy people write about sick stuff all the time - it’s just that you get the impression that he thinks his characters are normal, just more honest about what they want.