Did they purchase the books legally? Is their plan to destroy every copy of every book ever, and if it were, would that even be possible?

Its private property. I don't like it either, but I wouldn't like intrusive laws either.

I can destroy anything that I own. So can they. They're despicable for doing this, but there's nothing remotely illegal about it.

Not everything bad should be illegal, because sometimes outlawing a thing can have greater adverse consequences than the thing itself. Some things are better handled through social rejection.

There is no law about destructively scanning your own books. If you would like to preserve a book, buy it and send it to the Internet Archive for non destructive scanning and long term physical archival. It's very easy to do so, as someone who sends them books.

https://help.archive.org/help/how-do-i-make-a-physical-donat...

https://help.archive.org/help/does-the-internet-archive-have...