I loved practicing/reading about BDSM before I was 18. I'm 21 now, but that doesn't mean that I don't find what I did then erotic.
I find censorship of "young" erotica absurd for that very reason. Maybe some of you never had a single sexual thought before you were 18, but I strongly doubt that is the case for all of you.
Ya, so "exploitation of children" has another aspect. The part about some "children" considering themselves adults, or at the very least mature.
That said, I haven't had sex with anyone under 18 since around when I turned 18.
I do find the idea of sex with babies and children disgusting, much like scat, snuff, castration, and most other kinds of mutilation. But to paraphrase someone above, 'I'll still defend your right to write about it'
I'm rambling on. My point is that underage sex was one of the best parts of being under-age, and that was real life! What harm can come from a few stories?