As far as I am concerned: If it's a fictional story, anything goes. Literally anything. Child abuse, rape, murder, torture, genocide, racism, emotional exploitation, psychological warfare, any sort of cruelty - and of course compassion or love - is acceptable in a story.
The question is: is this plot device being used by the author in a good way. To make a point, to make the reader think, to build up the foundation of the fantasy world the story is told in or simply to open a new branch in the story telling?
Or is it used in a bad way, to appeal to the existing fantasies of a niche group of people?
I say bad, because that is my opinion as to what constitutes a "bad way" here, but strictly speaking, both choices are equally valid. The thing is: No one forces you to continue to put up with it. If the story doesn't do it for you, you are free to stop at any point.
However, I've been surprised more than once here. Sometimes I've kept reading a book I thought was rather disappointing only to find that suddenly things that have irked me beautifully come together at a later point.
A story is in part what you make of it. If you feel uncomfortable reading a book, you should stop there for a second and reflect on that.
Why do you feel uncomfortable? What are your values that the book is violating? Maybe entertain the thought of imagining yourself in the different available perspectives in the situation at hand. A book can be much more than the story it tells, really. You just need to be open to imagination.
Of course, I have been left feeling utterly depressed more than once doing that. But I have also felt exhilarated, inspired. Sometimes it made me forge new moral values or even change existing ones. Fictional stories have in no small part contributed to my world views, simply by contemplating the actions of characters, their individual situations, circumstances and relationships.
In that sense, even a poorly written book can hold surprising value, which is why I rarely drop a novel series at all, and I can't remember ever stopping to read a book because of extreme content. If anything, I stop reading books if there is constant repetition.
