i just want to clarify what you think would be so wrong with a service where you can find a book title, check out a scan of that book -- which has a corresponding physical copy in the real world, a one-to-one mapping to a physical book that is taken out of circulation -- and read it, while others cannot (because only one person can read that scan at a time), and then when you're finished, leave it for another person to read next.
And if that's wrong, is me lending a book to a friend wrong?
The thing that's a little tricky here, is in practice you can pretty easily keep a copy of that scan. It makes subsequent infringement a whole lot easier than checking out the book from a library or borrowing a physical book from a friend, because the thing that's an impediment to casual copying (scanning) has already been done.
And if that's wrong, is me lending a book to a friend wrong?