many people write just for themselves, no one else ever sees the stuff... but they write nonethless.

I've written one piece of fanfic; it was 25 years ago and has never seen the light of day.

Of course, every author has a right to determine whether they do or don't want fanfic written about their characters, but I don't see that fanfic has hurt, say, the Star Trek juggernaut or the Harry Potter books.