It seems like sacrilege to some--you cut up a BOOK? But for altered book artists and collagists, it's part of the creative process. How do you move from horror to the knife--or do you? What books are off-limits? Where do you get your choppable old books and magazines?
Here's one bit of comfort for the squeamish: the books at thriftshops are fair game. Why? Because their next stop is the shredder. Anything, ANYTHING you can do with a thriftshop book is rescuing it from a worse fate, guaranteed.
Here's another bit of rationalization I find useful: Some books NEED to be hacked up and off the shelves. I've been altering a dental anesthesia manual from the 1970s. It's actually got passages about how some racial/ethnic groups have higher pain tolerances than others....yikes! So anything I can do to get that thing way, way, WAY out of circulation, I'm happy to do it. It's worse than useless--it's outdated and racist 'medical' literature that needs to be gone.
Books I wouldn't cut up: anything older than 1900 (those are antiques); books with beautiful binding (they're already art); old yearbooks (I'd eagerly scan the images, though).