I love the fantasy forum on the Nanowrimo boards. It's lively and crazy, although often you will get something rather clueless like "How long should elves live?", "Can a demon do crocheting in his spare time?", or "Should I put an eight-legged banana in my Lovecraftian steampunk super-duper planetary romance orc-slash epic?" The answer is always: do whatever the hell you please. 'Cause it's your novel, not the Queen of England's.
One thread asks a similar sort of question but is interesting because of the way people are responding. Some people are replying in a writer's standpoint while others reply in a reader's standpoint because the question sends out mixed signals. (Although one could argue that this is a silly question that gets asked every year and answered the same way as well.) The thread simply asks in its title: Sex in a novel?
Those who are less squeamish about sex or are more open in their interpretation of what constitutes a good book go with the notion that if the story calls for a sex scene, then go ahead and write one in. If the story's focus isn't on somebody's relationship, then a sex scene would be out of place. The other view is reader-centric and depends on the reader's preferences. Those who like sex scenes say that sex is a natural part of human life and should be depicted in the course of human interaction. Those who dislike them say they are needless (and possibly drag out their own moral objections to it as well while they stomp all over an entire genre).
If a writer reaches a point while plotting or writing his or her story and must ask, "Should I add a sex scene here?", the writer must also ask, "Does it make sense to do so? Is it necessary to the development of the story?" If the answers to those last two questions are "no", then don't add it. If it will contribute to the story arc, then go ahead and have at it. Also note that I did not say that people should not write it if they feel uncomfortable. If writers only wrote about what they felt comfortable with, all the stories in the world would be as bland as oatmeal. (Of course, if you want to write a story as bland as oatmeal, that is your prerogative. No one's stopping you.)
In my view, sex is a plot and characterization device that must serve the needs of the story if it is present. It is not an element that can be declared as essential as the words themselves. It is also not an element that can be called taboo--as this infringes on other people's rights to say and write what they wish. If the question "Should I add a sex scene here?" posed to readers, one will get as many answers as there are readers--especially if the reader has no knowledge of the novel in question. Some people like them and some people don't. And yet for still others, it depends on the context.
(As an aside: I'm really annoyed when people try to convince others to omit things without knowing what the story is about and how it is written. I dislike violence, stupid characters, and time travel explained by woo-woo, but I'm not telling authors to get rid of that stuff. As a reader, one has the right to say that they dislike things and to not read books they feel they might dislike. A reader, however, does not have a right to dictate a writer's creativity whether it's writing sex scenes, steampunk, or both--even if the reader is another writer.)
The challenge for the writer then--if the writer is not writing the story solely for herself--is to figure out what market to pay attention to. I think this can be best accomplished not by asking random people on forums (trying to please all readers will be suicidal) but by reading the best books in the genre that you are writing in. How can you make that type of book better regardless of what sort of scene, plot element, or character added to the story? Would you read it if it had that particular element?
