I wrote a similar essay when I first started writing fan fiction, with a lot of the same points! It's so hard to cover everything that it could be, even when we try to figure out all the different mentalities that might bring people to slash.

I think everyone does. It's sad, because I am not even that new to fandom anymore.

I find it difficult to really buy the "our canon doesn't have good female characters" argument, if only because of this conversation I once had with my slash partner-in-crime:

Z: You know what's weird? I like 'Firefly,' but I'm not that interested in reading fic for it.
Y: Yeah, there's some slash, but I don't really have a favorite pairing.
Z: I think there's just too many strong interesting women.
Y: Yeah, damn them!
[Z and Y go back to reading SGA fanfic.]