It's not just that it cuts into sales of the original, it's that the author should maintain control of their work. If I write a book, a movie adaptation doesn't

It's not just that it cuts into sales of the original, it's that the author should maintain control of their work. If I write a book, a movie adaptation doesn't cut into the sales of the original. If anything, it'd probably increase them. But it's my story so I should be able to control who gets to make the movie adaptation. Otherwise I can write a book and anyone can immediately turn around and make it into a movie, owing me nothing. Heck, a third person could come and make a sequel to the movie, paying nothing to me or the first filmmaker. I think the only exception to this is the statutory licensing for music rights. Not the sound recordings, mind you. But that composition rights. Anyone can cover Taylor Swift (like Ryan Adams) so long as they pay her the compulsory license fee.