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.
Buying used copies of books, scanning them, and printing them and selling them: not fair use
Buying used copies of books, scanning them, and making merchandise and selling it: not fair use
The idea that training models is considered fair use just because you bought the work is naive. Fair use is not a law to leave open usage as long as it doesn’t fit a given description. It’s a law that specifically allows certain usages like criticism, comment, news reporting, teaching, scholarship, or research. Training AI models for purposes other than purely academic fits into none of these.