This is a well-known article on fanfiction and copyright. Rebecca Tushnet makes an argument for fanfiction to be an exception to copyright.
http://www.tushnet.com/law/law.html Scroll down to "writings" and click on "Legal Fictions: Copyright, Fan Fiction, and a New Common Law". It's a 38 page PDF but the print is large and the text itself accessible to a lay reader.