I've always found that 90% of fanfic is dross, 5% is interesting, 3% is bloody good and 2% is better than the source material. There is some pretty shabby stuff out there (pornish and otherwise) but by and large, I've always found that fantasy (by which I mean here sexual fantasizing) writing, even of the more extreme variety, does not translate into actual similar or even remotely-inspired conduct. So it's pathetic? Most people's writing abilities, let alone interior life, is pretty pathetic.

That being said, just when I had decided I LOATHED any idea of RPF for pretty much the reasons you said, someone wrote the most amazing Peter O'Toole/Leni Riefenstahl fic, Black and White, Still. Which basically proved again that you can write absolutely ANYTHING, as long as you have the talent to go with it.