Fan fictions are illegal, as they violate the copyrights of the series they imitate. Fan authors are not allowed to make a profit from any of their writings, and they can technically be required to cease and desist in their use of the copyrighted materials.
Questions of intellectual property are far too vast for me to possibly look at them here. Let's just acknowledge that there is a question, and move onward, shall we?
Right. As far as Star Trek goes, and most other areas of fan fiction, slash writers have almost as much - or even more - of a problem being accepted by those who share their fandom interests as by anyone else. Their work has historically been dismissed, at best as an unimaginative infringement of copyright and at worst as blatant pornography. Most of the authors write under pseudonyms. I emailed several slash artists and writers to get permission to use their work on this site; most didn't reply. One artist requested anonymity, saying that she knows people at the university who might see this presentation, and she does not want her hobbies publicly known. Another refused to let me use her artwork, saying that she feared repercussions from commercial studios.
"I thank the net for opening my mind but I know that many of my
peers have not had the same awakening. I probably wouldn't have been open
to the idea unless I'd slowly discovered it for myself so I don't expect
them to simply welcome it because I say so...I don't go out of my way to conceal it. If a housemate comes in and I'm working on a picture, I let them see it and then try to gauge their
reaction for future reference. Usually it just makes people uncomfortable
and what's the good in that when I have to work with them day in and day
out?" -- slash artist, name withheld.
One well-known commercial Star Trek author whom I e-mailed -- and who shall also remain nameless on this site, to avoid anyone spamming him -- responded, quite politely, that he didn't understand why I was wasting time with studying "garbage" when there was so much quality writing in the officially published Trek universe, and referred to the concept of slash as "uniformly sick".
The publishers themselves have an official policy against fan fiction due to the legal issues. John Ordover, the Senior Editor of Pocket Books' Star Trek section, responded to my question about slash in particular with: "The response is no different than to any other fan fiction. It's a copyright violation that we cannot condone. No more or less.:) Taking copyright out of considering, we just don't care one way or the other.:)"
Several authors who participated in writing for slash zines - like Jean Lorrah, A.C. Crispin, and Diane Duane - have had (non-slashed) Trek novels officially published, and gone on to successful writing careers. Some commercial authors reportedly still participate in slash writing using pseudonyms. (Penley 112)
No slash writer really expects that the themes they explore will ever be produced as part of their favored setting's canon history. But perhaps that's the wrong way to approach a question of validity. Is a concept like "The Cosmic Fuck" part of the official Trek universe? No.. so if Paramount Studios and Pocket Books decide what's "real" Star Trek, then slash certainly does not fit. However, is slash "real" in terms of being a valid expression of thoughts, feelings, and issues? Certainly. Perhaps it's more important to look at what is being said than what is being appropriated. Whether the stories are taking place in Star Trek, Blake's 7, or The X-Files, the themes seem to remain the same. Which brings us to our next section...