Many people write fanfiction. Generally, such writers are fans of the work they are writing about. Generally, yes, but not always. Some people are fine with viewing and producing fan-made media without being overly familiar with the source material. There can be any number of reasons for this. For instance, someone could be introduced to a fandom at a time when the series in question is not readily available (most commonly seen with anime and manga). Alternatively, someone might have been attracted to the fanwork scene by only a single aspect of the original work. And in some cases, someone might have been introduced to the franchise through its fanwork and never take much interest in the franchise beyond that. For some reason, this tends to show up more often in works that have lots of male characters. Needless to say, this can easily result in copious amounts of Fanon and Canon Defilement.