Personally I think there should be some sort of copyright law regarding fanfiction. The only author I know of who actually enjoys reading her fanfiction is JK Rowling, but then she can afford it. From what I've noticed about fanfic sites, it seems like Harry Potter fans, unlike many other clearly establish that their work is fanfic and the copyright is owned by JK and Bloomsbury etc. Alot of fans of other books just seem to write fics without any spoiler warnings or give the original author their due right. There is an upside and a downside to everything. I'll admit that I've actually read a series after reading fanfiction just to see how the original universe is. In it's proper place and with due copyright notice, I think fanfic can be a benefit to an author as long as the fanfic author realises that legally whatever they print belongs to the original author. Well written fanfiction just adds to the original story sometimes. But then that's just my opinion.
One could wish this was the case!
If there was a way for (not for sale) fanfic to be admissible without compromising the ACTUAL copyright of the work, that would be a delight.
It is the way the law applies that creates the problem - and makes fanfic the liability that it is, and must be treated as.....a case of a law creating an unintentional impact, perhaps - though I will admit there are so many angles, and I am not seeing all of them, not even close.
(not being, say, for example, a movie producer getting investors, and committing millions of dollars and hours of talent into a new production, and needing to protect that effort of creativity and lucre....)