courts tend to give greater protection to creative works; consequently, fair use applies more broadly to nonfiction, rather than fiction. Courts are usually more protective of art, music, poetry, feature films, and other creative works than they might be of nonfiction works.
Courts have ruled that even uses of small amounts may be excessive if they take the “heart of the work.” ... Photographs and artwork often generate controversies, because a user usually needs the full image, or the full “amount,” and this may not be a fair use.
(Keep in mind that many popular AI models have been trained on vast amounts of entire artworks, large sections of text, etc.)
Effect on the market is perhaps more complicated than the other three factors. Fundamentally, this factor means that if you could have realistically purchased or licensed the copyrighted work, that fact weighs against a finding of fair use. To evaluate this factor, you may need to make a simple investigation of the market to determine if the work is reasonably available for purchase or licensing. A work may be reasonably available if you are using a large portion of a book that is for sale at a typical market price. “Effect” is also closely linked to “purpose.” If your purpose is research or scholarship, market effect may be difficult to prove. If your purpose is commercial, then adverse market effect may be easier to prove.
To me, this factor is by far the strongest argument against AI being considered fair use.
The fact is that today's generative AI is being widely used for commercial purposes and stands to have a dramatic effect on the market for the same types of work that they are using to train their data models--work that they could realistically have been licensing, and probably should be.
Ask any artist, writer, musician, or other creator whether they think it's "fair" to use their work to generate commercial products without any form of credit, consent or compensation, and the vast majority will tell you it isn't. I'm curious what "strong argument" that AI training is fair use is, because I'm just not seeing it.