I think for a lot of people, it's simply the garbage quality of the writing and story-telling. (The New Yorker review, for example, humorously suggested, "No new reader, however charitable, could open '50 Shades of Grey,' browse a few paragraphs, and reasonably conclude that the author was writing in her first language, or even her fourth.")

Books often don't get much cultural attention, particularly on this scale. When something so sub-standard captures the public's imagination, it's at least a little disappointing for some, particularly when there are plenty of examples of well-written erotica available - the Sleeping Beauty series among them. The magnitude of the hate is probably proportional then to the popularity of 50 Shades of Grey. And we're seeing the same thing happening with the movie. Just like people point to the Sleeping Beauty series as an example within the same genre but done well, I keep seeing people point to Secretary as an example of a film that explores S&M in a more sophisticated and compelling manner than 50 Shades of Grey. I haven't seen it, so I wouldn't know.

I have, however, read both 50 Shades of Grey and the Sleeping Beauty series. While I think the latter is far superior to the former in terms of writing quality, I can see why 50 Shades of Grey is so much more popular: it's just female porn, and like all porn, it's aimed to titillate it's audience in a very blatant, obvious, and unthoughtful way. There's no more reason to expect it to be of high - or even adequate - quality than there would be reason to think that Internet porn should have the same level of production values, acting, or story-telling as a film premiering at a major film festival. They're just not the same thing, and the superior quality of one does not make it more likely or deserving of popularity than the other - as much as many (including me) would rather this not be the case. It's probably the same way a foodie might get frustrated - to no avail - that McDonald's is the most popular food in the world. (And hey, I can admit it. I like McDonalds. But I know enough not to claim that it's good food.)