Mostly due to mental disorder. A rare few people are born with a propensity towards it, but in a healthy society the idea would be so taboo that they would rarely, if ever, follow through with the impulse, and would eventually adjust to normal, societally approved, patterns.
Agreed, the same as pedophilia or any other perversion. They've done nothing wrong until they act on it. They need help, and while you may not be able to "cure" it you need to help them deal with it and not act on it. If you want to call it celibacy then so be it.
