There is a post in The Spectator regarding the view of books as semi-precious objects. He gives the example of a guy who buys cheap paperback versions of classic novels - then rips off their covers so they'll fit better into his back pocket. The Spectator goes on to defend this attitude, with the fact that books are no longer made by hand and hard to come by. Therefore it's not necessary to be so precious about them.
I'm one of those people who really hate marking books with pencil, much less tear pages out of them. In general, I just love books as objects (even notebooks and other stationery - but that's another fetish story).
Well, there was one exception...
Once, I went to Bolivia and Peru, with a short break in Buenos Aires, for a 5-week holiday. I wasn't able to find a Lonely Planet guidebook which covered only those two countries. Eventually I decided to buy their guidebook on the whole of South America, but it's a really thick book. So, after much agonising, I cut the book down the spine into four sections. This meant I could take just the portions which applied to Argentina, Bolivia and Peru, and saved me half of the original bulk. And I did get disapproving gasps from people who saw how I'd mutilated a Book.
On the whole though, I really hate when people borrow books from the library and fold down the corners instead of using bookmarks. Or even worse, cut or tear out pictures or whole pages from library books and magazines.