It was fun and fascinating to trawl through Yahoo Groups and sometimes something fascinating could be found. It wasn't the subject itself, it was the weirdos and the number of them. Too many and it gets hard to follow and it gets too impersonal to them, too few and no one will be active. 10-15 of them into something very niche sexually seemed to be the sweet spot, they became familiar and formed more personal bonds with each other while leaving the group open hoping that someone else would join them.
As individuals they could be wildly different people from each other and would never encounter each other in real life, they just had one specific thing in common. It sometimes reminded me of the serial killer convention in Sandman.
The thing that made it really fascinating to me was that these groups sometimes took the role of really sad support groups, it was like sneaking into an AA meeting and hearing their stories, what they think set them on this path, what disrupted their childhood and how lonely it was even if they had perfectly ordinary lives.
This was how I found the necrophiliacs and their discussion group, that's where I learned that a common theme was that they started as foot fetishists but didn't know why at the time. They weren't young people, 30-40+ in age, so they had thought about their unnatural lusts and how it worked for many years and it was a small group so they shared intimately. The way they figured, from personal experience, it went something like this: If the head, brain and face is the person the feet is farthest away from that and therefore the most impersonal, like an object. Removing the feet from the person/body made them actual objects. The next step in the discovery would be to realize that a body without a person inside it, a dead body, is the ultimate object or even a fetish in the more traditional sense.
Not clinical psychology in any way but that seemed to be the journey for a few of them and all these years later I'm still suspicious about foot fetishists.