If you do this, make sure it's deep in the middle somewhere and not easily seen via flipping through. Hotel bibles are provided by Gideons, and if you deface/destroy/remove/throw out/etc one, it'll just be replaced with zero fuss and no effort. The more people doing this, the more they replace, the more they print, etc etc.
It's always a great feeling taking it and wanting to wipe your arse with it, but 10 mins after you vacate the room another copy will be there waiting for the next person regardless of what you've done.