Would you be fine if they were derivative of your work and their sales (in the case of a commercial project like the one in this article) cut into your bottom line?
A lot of sold works are comparable to badly written fanfiction with inly a thin pretense of originality.
Popular conceptions of fantasy races (elves, dwarves, goblins, orcs, trolls, etc) are heavily indebted to Tolkien's portrayals of them in his works. While many of them were based on concepts from European (and especially Scandinavian) folklore, Tolkien's representations of those races were much more specific and different in character.
For instance, folkloric "elves" ranged anywhere from midgets to fairies to demons. Tolkien's nature-attuned immortals were a substantial departure from these traditions, and have suffused popular culture to the degree that they're now the default interpretation of "elf" in most contexts outside Christmas. The "orc" is an even more extreme example; the word was attested in some Old English texts but was long extinct in English by the time he borrowed it for a race of evil creatures in The Hobbit.
Pokemon games are a great example of people buying it for the (copyrighted) characters, while the (not-copyrightable) gameplay constantly gets criticized. A game that copies the monster designs while improving on the gameplay would cut into sales. Other games inspired by Pokemon never have as good monster designs.
A fan fic is ultimately just a subpar copy.
Dismissing works like A Fox In Space (aka Starfox The Animated Series) as ‘a subpar copy’ is ridiculously ignorant.
How does that work? Are you suggesting people will buy this book instead of lotr?
But to answer your question. I'd be fine with my great grand kids making their own way in life rather than living off my creation to the detriment of the rest of society.