Devils advocate here.
First, these are high school students, if they're not already sucking and fucking each other, they've already watched it all go down on the internet-enabled iPads you gave them as toddlers to shut them up.
Second, removing every book that has any description of sex or a blowjob would leave you with a giant hole in your fiction section. If we're going to remove anything a pearl-clutching parent could take offense to, we might as well just have encyclopedias (as long as they don't mention sex).
Third, reading this book is NOT going to turn your teenager gay, or incestuous. It just doesn't work like that. If you did anything to raise your kids you shouldn't be afraid of them reading fiction. Just words.
Fourth, BANNING BOOKS IS BAD. Banning literature is a tool of control. Literally 1984.
Fifth, there are some people with situations in their life that may benefit from being able to identify with the characters in this book. Maybe they have had someone in their family act inappropriately with them and don't know how to process it.
Sixth, no one has to read it. No ones being forced.