It is. I've never met anyone in my country that wants to prevent adults from reading any books. We do have some people that want to prevent children from reading books that contain images of child pornography.
In fact, our most banned book is such a book. It's called Gender Queer and it's banned for containing images of children engaged in oral sex with each other. Some parents don't want children to see one child's penis penetrate another child.
https://www.ala.org/advocacy/bbooks/frequentlychallengedbooks/top10