Libraries are book-lenders.
If you want to own a book you have to buy it...that's the difference. I think I'd lik to keep it that way.
Imagine what would happen if everybody could just grab a book from the library for free (or for the few bucks a library membership costs per year) and keep it.
Bookstores wouldn't make any more profit, authors wouldn't earn much...so in the case of libraries a "countdown would be cool...you could still "own" the book by borrowing it again and again, but that wouldn't be worth the hassle.
You borrow a book, read it and it "vanishes" or expires and doesn't take up any space.
If you want a book you really love and read and reread it over and over again or use it as a reference work for an ongoing project you can buy it.
Where I see DRM as impractical is with books you buy. I don't want to have books I'll always have to be afraid will suddenly stop working if I put them on another device or store them in a backup folder somewhere.
I buy a paper book and can do wahtever I like with it including reselling it (with ebooks you have the problem that you don't lose the book if you resell it...but I doubt this would be a large-scale problem anyway) and tearing it apart and using hte pages as toilet paper.
Any DRM that makes ebooks more restrictive that paper books is bad.
End of Story...for me at least.