Many years ago I read a collection of stories that had not been published, not because of their quality but because of the challenging themes.
I am trying to remember the name of the story, and its author, that begins with the hero helping some traders that were being robbed. The traders are selling some metal that is vital to everyone, but no one wants to acknowledge it, as the planet where it is mined the inhabitants practice incest. The hero travels to that planet, falls in love with the daughter of the trader, and stays in that planet. Anyway, the story discusses race improvement through inbreeding.
The editor of the book, if I am not mistaken is Isaac Asimov. Or at least, he wrote the introduction to the collection. Many of the authors in that collection were award winning.