I tend to fall on the 'Nature' side of things, as opposed to, 'Nurture' when it comes to what drives a person's failings. But having said that, in most of these cases I think you have to have the genes for this and be raised incorrectly somehow. So a combo is usually required IMHO.
I simply cannot comprehend how any adult, man or women, can look at a naked 12 year old and somehow get turned on by that. But that happens. Same applies to looking at another grown man. I just don't have that in me and simply can't relate to it in any way. The people who do this stuff have something inside of them that most of us don't.
But it doesn't surprise me that these people are good at hiding this side of themselves. Everyone has a secret side that no one knows about. Sometimes that secret side is really, really bad. Had a GF like that once. No bueno mi amigos!!