This is the short version:
John Steakley’s novel Armor is NOT Starship Troopers fan fiction.
Robert Heinlein’s Starship Troopers is NOT Lensmen fan fiction.
Charles Stross’ fantasy novel The Family Trade is NOT second-hand fan fiction of Philip José Farmer’s World of Tiers.
The Lord of the Rings movies are NOT fan fiction of J. R. R. Tolkien’s novels.
Novelizations of movies are NOT fan fiction of those movies.
The new Star Trek movies are NOT Star Trek fan fiction.
Diane Duane’s novel The Wounded Sky is NOT Star Trek fan fiction.
See a pattern here? Merely being inspired by something else doesn’t make the inspired thing fan fiction, nor should derivative work be confused with fan fiction. Fan fiction is, by definition, a form of derivative work, but not all derivative work is fan fiction, not even when the person responsible for the derivative work is a self-described fan of the original. The existence of authorized derivative works does not mean it’s okay for everyone to publish fan fiction of whatever they please. It is wrong to use the existence of authorized derivative works to justify stealing another’s creations with ‘its all fanfic, i can write what I want lol!!!’
There will be a longer version of this post later…