A lot of the time, when people find a book offensive or insulting what they object to is its premise. This is true of stories set in the American civil war about slaves who fall in love with their masters. It’s true of stories set in the Second World War about Jews who fall in love with concentration camp commanders. It’s true of stories set in alternative universes in which the Native Americans are erased from history in order to allow white settlers to have exciting adventures with mammoths. If your complaint is “I do not want to read a book about this thing or in which this thing happens” all you need to know about the book is that it is about the thing or that the thing happens in it. There is nothing you can learn from reading the book that would address your primary concern.
Of course, there are always exceptions and edge cases. It is, theoretically possible, that you could write a romance in which a black slave falls in love with a white slave owner that is actually a searing indictment of the way in which the history of slavery has been appropriated by white people in order to tell stories that make them feel good about themselves. You could write a love story set in a concentration camp that is about the way in which the Holocaust is used by people who never experienced it and were not affected by it to push agendas and narratives that personally suit them. Or the way that Jewish stories have historically been appropriated by Christian culture.
But, first of all, I’d probably only try to write a story like that if I was (depending on the context) black or Jewish and, secondly, the “you haven’t read it” argument is never actually used in this kind of situation.
Alexis Hall on bad arguments.