I'm guessing what you're going at is repressed desires and/or early childhood desires.
For me some of it is, some of it isn't. For a fetish I will leave unstated, I think I have traced it back pretty solidly to early childhood, the only question was if there was a specific trigger, which I did figure out.
For other things such as furry, even though I see an early obsession with anthropomorphics, at least to where I can remember at about 5 years old, I think it just developed into a 'fetish' later. Some people would even call what some of us have as an 'orientation' rather than a 'fetish' within the furry fandom.
I'm not willing to go that far on it, but I'm pretty sure my more adult interest in furry is just a natural extension of a time and money consuming lifelong obsession. Some people spend lots of time and money on another person before using them to get off (I know I have a bitter sense of what love is). I spent a lot of time and money on bringing a character to life, so now I just use that.
I agree with Fallowfox's idea of programming bugs, the only question left is when they were made. Unless there is another reason you have to uncover what happened though, it's not worth the 5 years of professional therapy needed to find them. If you didn't need all that just to figure it out, you would have been able to find out yourself by now. It's just not worth it without another reason to go after the knowledge.
I'm pretty sure any sexual interest I have in furry developed pretty innocently over the normal course of time. My other one is a different story, I did go through a few years of B.S. to figure that one out, but it was worth it, because something major was actually behind it. I just had to follow my intuition on it.
I'm sitting in a public library right now, browsing this site, even looking at porn on FA, and wearing a dog collar, and nobody cares (I do live in the San Francisco of the Mid West though, I'm the normal one). My other fetish, although safely enjoyed by quite a number of people, I couldn't manage to enjoy in such a normal and safe way, without it intruding on my life, due to it's background which I discovered a few years ago. It's all a very personal matter.