writing sex scenes... why?

Fiction writers are familiar with the fallacy. Readers attribute details and events that happen to characters in fiction to the writer's own experiences and life. A character in a novel has a dog. The writer receives handsome leashes and cute doggie toys from admiring readers for a dog she doesn't have. Etc.
I'm guilty myself. I recently read a novel by a woman whom I only know via a mutual friend. One of the male characters in her book bears a copycat physical resemblance to the man in her life. It was hard, while reading, not to imagine the two characters in the book as the real-life people. (Which is not as easy as it sounds--holding up such an exacting mirror to create characters. Personally, I prefer making up characters to copying people.) Then I got to the sex scenes.
That led me to wonder about readers of my fiction attributing the dialogue, habits, opinions and activities--including sexual--of my characters to me. I hope they don't and wish they wouldn't. I don't want them thinking they're eavesdropping on my supper conversation. I certainly don't want them in my bed! The best way to avoid the latter would be not to write sex scenes. Well, sure.
Except that sex is such an interesting way to explore character. The buttons that push sexual appetite are deeply rooted in the psyche. And what about that sinuous relationship between the language of sexuality and self-image? Sex can reach back into apprehensions/discomfort/knowledge/promptings a character didn't understand as a child. Haven't you had sex with someone who's acting out a fantasy that has nothing to do with who you are? What's that all about? Some characters feel comfortable about sex, some embarrassed. For some, it's an enjoyable way to relax, a furtive act best hidden, a game, a hygienic exercise, fraught with worries about getting pregnant. And oh, yes, love. Sometimes sex is an expression of love, which is another weird equation that doesn't always add up.
Among the many facets of character that are available to explore, sex is one of them. So that's why my characters will continue to be sexual beings, as well as beings who go to work (or don't), buy groceries, climb ladders, have allergies...
Which brings me back to the top. Do my characters act and think like me? I've written too many characters by now. Opposing types, different genders, various ages. They can't all be like me! No doubt some of them have traits I share, but mostly I like to make up characters and stories.
In grade school a teacher wrote on my report card: "Alice has too much imagination." She meant it as criticism. It wasn't the kind of school where teachers were on the lookout for fledgling artists or writers. Quick instincts on the soccer field were more important.
I'm no good at kicking balls. I'm glad my imagination survived childhood.