I guess I was put off Fan / Slash Fiction slightly when someone sent me a link to a story that turned out to be a highly improbable piece of magical realist porn featuring several Man United players. Shudder.*snort*
It DOES sound grim doesn't it!?
On a more serious note, the original piece by Jessica Reed does raise some interesting points about fan-fiction. I'd only make one proviso and that is 'why does it have to be the preserve of teenagers'? For sure, she's starting from a standpoint of reading RL/character or celebrity fic which generally runs to different expectations. But where writers online take existing characters and build new narratives, these can often be incredibly well produced: polished, edited, copy-checked, and critiqued giving eager readers extended scenes, alternate universes (not just as a sci-fi concept but, if you like, stories outside of the original realm of the story canon) and answers to 'what if?'
There's bad writing everywhere - much of it legitimately published. Just because its online doesn't make it bad, in much the same way that we may defend blogging...