Should I feel ashamed for writing fanfiction?
I'm not going to feel ashamed for writing fanfiction. My family was embarrassed for a while, that I had such a "juvenile" hobby when I could be doing "something more productive." They eventually learned that other people--college friends, admired authors--wrote and read it too. One of my friends took hers a step further and submitted a screenplay to "Star Trek:The Next Generation." She got it back covered with coffee stains and a nice letter indicating the reasons why it was rejected.
All those movies of Cinderella, and Snow White and so on that Disney did? fanfiction on the screen. Sherlock Holmes parodies, movies, and television shows are fanfiction. There are novels and comic books that started out as fanfics.
This, from Fanfic - TV Tropes:
The distinction between fanfic and original fiction, as we know it today, is largely created by modern copyright law; much of classical writing is actually "fanfiction" based on older sources. The major distinction between fanfic and a story inspired by another story is that the story a fanfic is based on has one or more "official" versions, usually owned by a company, a creator, or both. Thus, things like The Infancy Gospel of Thomas, a piece of biblical apocrypha featuring Angry!Uber!Baby Jesus, or variations on Arthurian legend where there is no Holy Grail and Lancelot's affair with Guinevere never happens, would not "count" by this definition.
No statement on the legality of fanfic has ever been given in American formal law or in its courts. Some argue that it's a form of copyright infringement; however, see "Legal Fictions: Copyright, Fan Fiction, and a New Common Law", and note the above precedents. The two most common arguments for fanfic being legal involve either implied consent - companies and authors have every right to enact a Fanwork Ban as evidenced by http://fanfiction.net's banlist but are mostly tolerant - or fair use - the non-profit, educational and transformative use of the work justifies its existence. The latter is the main argument that sparked the development of the Organization of Transformative Works, a fan labor advocacy site.