I'm working on a sequel to Dostoevsky's The Brothers Karamazov...I think it's going to be a huge hit.A (probably uncommon) opinion of mine is this:
"Fan fiction" is usually ethically suspect, unless the author is given the opportunity to approve of it (or not). Fan fiction hijacks somebody else's world, characters, fictional history, etc., and does things with these that the author did not intend.
"Fan fiction" has often been the polite label for literary vandalism.
That vandalism has usually been well-intended. But subjective good intent is a completely different question.
This literary vandalism is serious to the degree that the original art is great, and to the degree that the original author is unique.
Tolkien was unique in ways and on levels that few people even have categories to comprehend.
And he is not around to approve of what others are doing with his creations.
If somebody wants to make films and shows involving elves and orcs and reforged swords, that's fine, he can have fun. But he shouldn't freighthop on the train of Tolkien's world and countries and characters and names. He needs that Trojan Horse because he doesn't have the skill to garner fans on his own merits.
Ivan recovers and comes to terms with his latent homosexuality, Dmitri escapes to America and starts a Socialist movement as penance for his turbulent past, and Alexei converts to Islam.