I've never had sex or desire to have sex with my own family. But the idea of porn like incest (sister and milf stuff) appealed to me when I was younger.

I was very insecure, and opening myself up to people is still extremely difficult. Even in long term relationships I wasn't able to open up like they would to me. So having someone that already knew what the "real" me was like (real as in what I'm like when I'm comfortable at home) and still found me attractive enough to fuck, was very appealing.

So I guess it was less about the incest, and more about feeling secure, like they wouldn't run away when they encountered who I was behind the sociable persona because they had already grown up with that side of me and where attracted to me regardless.