Regular copyright law says that if you _buy_ a book, digital or not, you can resell it. If you license a book, digital or not, you can't except as specified in the license.
IA's point is that digital books (which are many or most books nowadats) aren't sold; instead, they are licensed.
https://www.justice.gov/archives/jm/criminal-resource-manual...
> Further, the privileges created by the first sale principle do not "extend to any person who has acquired possession of the copy or phonorecord from the copyright owner, by rental, lease, loan, or otherwise, without acquiring ownership of it." See 17 U.S.C. § 109(d).
Patents are explicitly covered there, too; from Art 1, §8:
"[the United States Congress shall have power] To promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries."
Maybe pedantic but there is no "intellectual property" law in play here. Just plain old copyright law, under which they do fully own the books - as opposed to licensing them. What copyright law allows is everything that libraries do.
My opinion - One should be able to use a webcam to share a book with someone. That's not far from what IA is doing though it's also technically quite different.
On another note, I'm not a fan of using the pandemic to highlight IAs value even though I appreciate their efforts.