Originally Posted by epiphany
Because they aren't going to miss it. A few bits of information on my computer will be different but the library is no worse off. This is self evident because they will never even notice whether or not I deleted the book. If my action has no potential to cause anyone harm then I don't consider it morally wrong.
It does not harm the library directly, but it can harm the authors. If you keep an ebook from the library, you will feel absolutely no need to purchase it in case you liked it. Whereas if you have to remove the ebook when it expires, you my feel it's more convenient to buy copy for yourself.
Of course, if you don't ever look again (and no one else does) at a file you should have deleted but didn't, there's no difference, but I don't think that's what you'd do.
It's a bit like having an affair and saying it's OK as long as your wife doesn't know...