Doctor Science considers the controversial rating from the perspective of a fanfiction reader:
As you probably have heard, a majority of fanfic involves romance and/or sex. Most fanfic is read and written by women, and despite the conventional wisdom that women “don’t like porn”, it’s usually the case that, all other things being equal, more sexually-explicit fanfic is the most popular. This has been known ever since the late 90s at latest, when writers started putting hit counters up on their websites and saw that stories labeled “NC-17” consistently got the most hits. Women definitely *do* like porn, as long as it’s the kind of porn they like.
In fanfictionland, then, “NC-17” is not at all the kiss of death it is for movies — on the contrary, it tends to pull readers rather than otherwise. NC-17, MA, Explicit are all marks of the good stuff, not marks of shame. People still like and read plenty of things that are equivalent to G or PG movies, but there is no shred of community disapproval (and plenty of cheers of approval) for extremely sexually explicit material, at least if it’s marked clearly enough that Net-Nanny-type programs can keep the kiddies out if their parents think that will work.