I’ve not only read both books the OP mentioned (“Beloved” and "One Flew Over the Cuckoo’s Nest), I’ve also I’ve taught one of them. The study of literature, especially novels, involves the study of human conflict. It is inescapable that immorality - in whatever form it may appear, and that is a HUGE spectrum - forms a basis for conflict. What about Shakespeare? Certainly, the murders and suicides in “Romeo and Juliet” are immoral, but the thematic emphasis is on the human conflicts which led to these acts. Shakespeare did not write this play for the purpose of luridly exploring immorality for its own sake; rather, ti is a tragic by-product of the conflicts. Likewise, “To Kill A Mockingbird” contains plenty of immorality, but it serves to emphasize the themes of injustice and innocence. The same holds true for “Beloved” and “Cuckoo’s Nest”. Are there novels (and movies, music, etc.) which simply exploit and glorify immorality in an offensive way? Yes. But a Catholic can take care to discern such things and read literature which contains immorality without risking the sin of scandal.