I don’t suppose erotic novels would get by without them, but what about the others? Literature from bygone ages wasn’t strong on such scenes since they were socially frowned upon, for example by people who felt it necessary to cover up table legs. We don’t live in such times now, but the fact that we can do something doesn’t mean it’s a good idea. We can sing to the moon but usually choose not to.
The main reasons for including sex scenes are that we are dealing with people, some of whom have sex, or that we want to move more copies of our latest bonk-buster. Ignoring the second of these, we could claim that the account of our characters’ lives is incomplete if we fail to cover this angle. Which is entirely logical but does have implications. People also relieve themselves, so do we describe this in great detail too?
Probably not. It isn’t an exact comparison anyway, since it could argued that the emotions are more involved in sex, which may be less necessary but is surely more significant than emptying the bladder or moving the bowel. So we accept this argument and dash off our sex scenes – only have them nominated for the Bad Sex awards. Because writing a sex scene well is by no means easy. I couldn’t do it, and many of those who attempt it can’t do it either. If you have that talent well and good: if you don’t you shouldn’t try.
And if you don’t, console yourself, you’re in good company. Is Anna Karenina any worse for the absence of graphic descriptions of Anna and Vronsky getting their kit off and going at it hammer and tongs on the chaise longue? Resting content with being suggestive rather than downright graphic is usually more effective.