It’s important in the fair use assessment to understand that the training itself is fair use, but the pirating of the books is the issue at hand here, and is what Anthropic “whoopsied” into in acquiring the training data.
Buying used copies of books, scanning them, and training on it is fine.
Rainbows End was prescient in many ways.
I could read a book, but its highly unlikely I could regurgitate it, much less months or years later. An LLM, however, can. While we can say "training is like reading", its also not like reading at all due to permanent perfect recall.
Not only does an LLM have perfect recall, it also has the ability to distribute plagiarized ideas at a scale no human can. There's a lot of questions to be answered about where fair use starts/ends for these LLM products.
The judge presiding over this case has already issued a ruling to the effect that training an LLM like Anthropic's AI with legally acquired material is in fact fair use. So unless someone comes up with some novel claims that weren't already attempted, claims that a different form of AI is significantly different from a copyright perspective from an LLM or tries their hand in a different circuit to get a split decision, the "jury" is pretty much settled on how fair use applies to AI. Legally acquired material used to train LLMs is fair use. Illegally obtaining copies of material is not fair use, and the transformative nature of LLMs don't retroactively make it fair use.