Comment by OkayPhysicist

There's a lot of conflation of "should/shouldn't" and "is/isn't". The comments by tech folk you're alluding to mostly think that it "shouldn't" be fair use, out of concern about the societal consequences, whereas judges are looking at it and saying that it "is" fair use, based on the existing law.

Any reasonable reading of the current state of fair use doctrine makes it obvious that the process between Harry Potter and the Sorcerer's Stone and "A computer program that outputs responses to user prompts about a variety of topics" is wildly transformative, and thus the usage of the copyrighted material is probably covered by fair use.