It is fair use to train on books you buy. The anthropic case established that. The destruction of books is just cutting the spine so they have individual pages to scan.
They are not destroying any books to make any claim. They are doing it so the pages fit in the scanner.
Without an example of an actual rare book that is shown to have been destroyed, all there is is the is the claim they have the capability to do that.
The closest I have heard is the possibility of rare books purchased in bulk orders of cheap second hand books. This is a similar risk to melting down someone's wedding ring from a batch of scrap metal. It could theoretically happen, but the knowledge of the items presence is absent and it was not requested.
What other allegations have there been? I'm prepared to look at actual examples of you have them.
