I think people get too wrapped up in situating themselves or how others would look down on them if they were to engage in such a relationship. First, these are fictional characters, it’s perfectly fine to enjoy the story when there’s nothing actually real in this story. Are there possibly situations like this that actually exist out in the world somewhere? Sure, I wouldn’t discount it. But they are not this particular story and this fictional situation has no baring whatsoever on your personal life in any way. Just because you are reading it and enjoying the story doesn’t mean you are going to suddenly go wanting to have a relationship with your own blood relative. That would be like saying reading a book about gays will make you gay, or the other way around, reading about heterosexuals will make some heterosexual if they already not. I think this is something to remember for the future for everyone that reads this or any kind of story.