Italian, I think you may have misunderstood several points in my post (possibly because it was so epically long - perhaps I need a good editor!)
I agree that the written word is different from film, for the reasons you say.
Also, when I said there were two theories, the "repressed desire" theory, and the Stockholm syndrome theory, I thought it was pretty clear that I favoured the latter as an explanation. NB, as a caveat, I'd say that I don't know where you're from. If you're based in Europe or the UK, your experience of evangelical Christianity may be very different from that of someone in the US. I had naively thought "surely no-one is that repressed" before I had long series of online discussions with American writers who felt they really had had their sexuality damaged by repressive religious attitudes - there was a very good blog post on this on the "No longer quivering" blogsite - which admittedly is about people escaping extreme religion, but I've also talked to women whose upbringing was much more liberal but still feel they were left screwed up about sex. America is a complex and varied country, and obviously attitudes in, say, San Francisco are going to be different from those in Little Bend, Michigan - but there are still pockets which are deeply socially conservative. I still think that the Stockholm syndrome explanation is more plausible, but in the light of conversations I've had with numerous people, I wouldn't completely write off the repression theory.
As for "no harm, except possibly the writer" - you're forgetting that this stuff is widely read too, often by teenagers (despite putting age ratings on it). In this respect it's shaping peoples' attitudes, though no more so, I would say, than back in my teens (a long time ago) when we thumbed through our mum's copies of Jilly Cooper and didn't realise at the time that the "coercive sex" was actually rape.
I should point out that I like a lot of fanfic, for the reasons Vestal alludes to - that typically one is already invested in the characters. "Non-con" is a small, but non-negligible proportion of erotic fanfic, which in turn is actually a minority part of fanfic as a whole (there's romantic but not sexual fanfic, and non-romantic fanfic out there too). I like "vanilla" erotica, and general fanfic - I just find the rape fantasies disturbing (I don't read them, but I am interested, as an intellectual, and feminist question, as to why women write it: why would women be complicit in and celebrate their own oppression?)
As to why I bother to write it when I'm not particularly good - why does anyone have a hobby that they're not up to professional standard at? People get pleasure from playing music without being good enough to make it as professional musicians, people get pleasure from going to art classes without thinking they'll win next year's Turner prize, people get pleasure from playing Sunday league football even though they're never going to be signed for a Premiership team - why should writing be any different?