These books were purchased by them before being destroyed in the scanning process. I fail to see the issue with this specific case. Lots of artists buy stuff and irreversibly modify it. Are we going to be angry now at people who glue their puzzles or use parts of books for scrapbooking? If these were unique works there would be an issue, but I don't think that truly unique pieces would be in their target group, as the destructive scanning is all about cost cutting and unique works cost a lot of money that they wouldn't just destroy.

The fact that they use it for model training and later sell access to that model's work is the shady part that has a severe whiff of plagiarism to it.