[recursivecaveat]

The "and then fed them into an AI" part of "facebook pirated a bunch of books and then fed them into an AI" part is irrelevant. It would be equally illegal if they pirated them and then sat around reading them. Unless you somehow hope that the entirety of copyright will be overturned by this court case (not a chance) then you should strongly hope that facebook loses, because the alternative is literally "rules for thee but not for me" where corps can pirate whatever they want, but nothing changes for ordinary citizens.