I'm convinced it's innate. I've never met my mother. I was raised by my father. We both knew from the beginning that this was not an optimal situation, especially since he was from an all-boy family, and had a long-simmering conflict wit his mother, but we both tried to make it work, and it did.
The good news is that I was allowed to self-administer enemas as soon as I moved from a training bra into one with some actual support.
My Dad had to take enemas entirely behind his parent's back, and learn about them the same way. His domineering Mom was as anti-enema as you could ever get, at least for boys, and the family was two parents and two boys.
Once my father realized I had the same love of enemas he did, he made sure I was NOT going to do them behind his back. We could openly discuss them, and I just had to tell him what I was doing.
Once while I was home over winter break from College, I even asked him why he was so tolerant about what a lot of people consider a sexual deviance. He told me about the secretiveness with which he had to use enemas, and told me that it was healthier, both physically and emotionally if I had good information from the beginning. He admitted that he did some unhealthy, and possibly unsafe things figuring everything out in his teens. He also thought he would have fewer bowel problems in later life, if he had been able to be more open with his own mom.
He did Say one thing at the end of that conversation. He said, "Honey, if two enema lovers hadn't found each other, you wouldn't exist! No sense denying who you are!"