A better analogy would be that you do original research or work and produce a valuable book. Somebody else looks at your work, decides it has value, and reproduces it in a new book under their name. The new book is cheaper, or easier to find, or for whatever reason displaces your original book created through your own research and investment. Now somebody else is profiting off your creativity or work, without payment or even acknowledgement.
I'm not sure how this plays out legally, but it certainly seems unethical
So for example, when Disney sees value in public domain stories like Cinderella, Rapunzel/Tangled or Snow White, and they make movies out of them, profiting from the creativity and work of the Brothers Grimm without paying anything to their estate, or high school plays do Shakespeare, that seems unethical to you?
Would it be fair for Greece to do retroactive term extensions all the way back to Plato and then sue anyone who copies the idea of having a university or uses the Platonic solids or distributes religious texts that incorporate the dualistic theory of the soul?
Your examples, as you say, are all public domain. Are all the works we train LLMs on public domain too? Was the original book in my analogy in the public domain? What do you think about training on material that isn't yet in the public domain?
You're framing this as an ethical question, but copyright term lengths are essentially arbitrary. They're set by the government, as are the boundaries of fair use. At which point you're making a circular argument. That it's bad if it's illegal and that it should be illegal because it's bad. So what happens if someone argues the opposite? That it's not unethical if it's fair use and then it should be fair use because it's not unethical.