Breen, after reading it himself, told Bradley: "Now you can write that story about the chieri that you thought you couldn't write". Bradley then had the idea to write The World Wreckers. Edmond Hamilton had been called "The ol' world wrecker" because he destroyed planets, galaxies and even universes in his books. Norman Spinrad had written The Doomsday Machine, but Bradley thought there must be more subtle ways to wreck a world, such as interfering with a fragile ecology. She also saw this book as the end of the Darkover series; a way to end it, like "tossing Sherlock Holmes off the cliff at the Reichenbach Falls". However, Bradley realized that she needed one fairly explicit sex scene to make the human-chieri interaction work. Don Wollheim reluctantly told her to go ahead, although he demanded that she use no profanity (which was not her intention anyway), and she demanded in return that he would not change it without consulting her. Bradley claims that the scene, which "shocked some people and pleased others", was the first time the issue of homosexuality (not to mention sex-changing) had been dealt with directly in science fiction, and says, "I managed to become something like science fiction's token homosexual!" After the success of The World Wreckers, Don Wollheim was more willing to publish material that would have been considered controversial before. In particular, Bradley mentions How Are the Mighty Fallen by Thomas Burnett Swann. But every time Bradley said that the Darkover series was ended, friends, fans and casual readers objected, "Oh, don't do that!" Themes Several themes are explored by Bradley at length within the books of the series. Psychic powers, treated as a science, are a theme that places the books firmly within the category of science fiction, even in the books that do not have "Terrans", spaceships, or the "Galactic Empire". They can also be called fantasy, because psychic powers appear to be "out and out magic". Other themes are feminism, sexism, the roles of women in society, the roles of men in society, racism, social division (the Comyn nobility and the non-Comyn "commoners"), xenophobia and the clash of cultures, sexual taboos, fate and the horrors of war. Feminism According to Nasrullah Mambrol, "though Bradley did not call herself a feminist, she was both criticized and applauded by those who have". Bradley received much criticism for her book Darkover Landfall because of