This article by Henry Jenkins-- author of Textual Poachers: Television Fans and Participatory Culture and the guy who wrote about Obama as a Secret Vulcan--is the smartest thing I've read on fan culture:
How to Watch a Fanvid
His explanation of slash is the only thing I've read that I would give to someone who just didn't get it. It ...well, here, I'm going to cut and paste this bit:
When I try to explain slash to non-fans, I often reference that moment in Star Trek: The Wrath of Khan where Spock is dying and Kirk stands there, a wall of glass separating the two longtime buddies.
Both of them are reaching out towards each other, their hands pressed hard against the glass, trying to establish physical contact. They both have so much they want to say and so little time to say it. Spock calls Kirk his friend, the fullest expression of their feelings anywhere in the series.
Almost everyone who watches that scene feels the passion the two men share, the hunger for something more than what they are allowed.
And, I tell my nonfan listeners,
slash is what happens when you take away the glass. [bolded by Fresca]
The glass, for me, is often more social than physical; the glass represents those aspects of traditional masculinity which prevent emotional expressiveness or physical intimacy between men....
Slash is what happens when you take away those barriers....
One of the most exciting things about slash is that it teaches us how to recognize the signs of emotional caring beneath all the masks....