In the case to which I assume you are alluding, Conan Doyle did not forbid the use of his invented world by those who wished to 'meta-fic'. I believe the real flood of such came after his death, however, even when he was alive, he indulged those who invested Sherlock with all the attributes of a living man. It may have annoyed him but he did not try to cut it off altogether.

Most writers seems to be charmed that their creations inspire the level of affection and interest which manifests itself as fanfiction. Those few who are offended and forbid such use of their creations should be heard - this is my opinion. My defense of fanfiction as a legitimate genre yields to my greater defense of an individual's privacy. If Anne Rice thinks she has sole title to her characters, I gladly grant her that. She has so befouled the vampire tradition, I loathe her anyway. ;) Vampires as rock stars! Hmph!