Pros and cons of fan fiction

As everyone should no by now fan fiction is a very extended activity nowadays. Now I'll proceed to open a debate:

Arguments for

Fan fiction is the perfect way to make the readers contribute to their favourite works,and also is a good chance for the readers because it's an opportunity to keep reading good sagas even if the author is'nt writing them anymore. There are a couple of cases where fan fiction feedbacks the story and the world that they're inspired in( Dragonlance), and that's a prove tha fan fiction can work.

Arguments against

Fan ficion is considered in many circles bad or disrecpetful, they say that because  it's obvious that the fan fiction works are not the same as the original saga, and because ih these days the fan fiction writers dare to tell the original authors what to do or what to write next, like "A song of fire and ice" case ( and that in my humble opinion is unacceptable)

Here are my arguments for and against fan fiction  the conclussion as always is up to you