The huge misunderstanding about copyright has to do with its intention and purpose. The intention and purpose of copyright as a legal right has to do with commercial gain, and not with ownership. The ownership of a work that is published is always limited - yeah, whether any of us like it or not, the right to the ownership of something is limited as soon as it is published, because it is sold to a publisher. It is THAT PUBLISHER, not the author, who retains the commercial right to the work, and it can only revert under contractual terms agreed with the owner who sells it to the publisher. At any rate, the ownership of any and all items that are published after 1978 revert to the public in an unrestricted manner - at least in North American, 70 years after the death of the author: see the following table
http://www.unc.edu/~unclng/public-d.htmCopyright is ALWAYS limited, however, and this right to publish for gain is constrained by the Right of Fair Use, as follows:
The right of criticism and commentary
The right of parody
The right of educational use
The right of noncommercial use
Yes, non commercial use. That means that if there is potentially NO IMPACT to the owner of the copyright by the use of the work, then it MAY be considered a fair use. However, in most cases of fan fiction - which is by definition noncommercial use - threats by copyright owners for protection of their copyright are not tested in court due to the potentially devastating effect of a negative judgement: $100,000 per incident if the judgement is unfavorable. The case of "The Wind Done Gone"- in which the estate of Margaret Mitchell sued Houghton-Mufflin was resolved after an appeals court vacated an injunction against publishing it, and the parties came to an agreement for Houghton-Mifflin to make a donation to Morehouse College, an African-American institution of higher learning. However, considering that the injunction was lifted, it indicates that Mitchell's estate was likely to have lost that lawsuit and so agreed to settle.
There is nothing in copyright case law to justify classifying fan fiction as copyright violation in its noncommercial form; only works that are not permitted by the copyright holder (not the author, please note, but the OWNER) which are published for gain are considered likely to be violations of fair use.
The purpose of copyright is not to protect authors and owners from the use of their property: it is to protect the commercial viability of their works for themselves.
At any rate, the unpermitted use of another's intellectual property is not theft: it is infringement.