This comes up all the time. People who dog-ear their pages, who make notes in books or highlight, or underline, are called “monsters” by a lot of readers.
No really, you tell me a book that sits pristine on a shelf, with an uncracked spine, pages barely touched much less wrinkly and stained by coffee or tea, pages without the occasional dog-ear or note, even if all it says is “YES!!!” You tell me that’s a loved book and I will tell you that you lie. It’s a worshiped book, maybe, but loved? No. Things that are loved are used and handled, and held close in sometimes sweaty or dirty hands. Books that are loved are read at the dinner table, dropped into the bathtub or off the side if the bed, sometimes left in the rain. They are companions, not barely touched treasures.
So by all means use bookmarks — I’ve used everything from old bus transfers to pens when a proper bookmark isn’t available, but I have also dog-eared and used dust jackets. By all means confine your commentary to a lovely journal or your Facebook. Just don’t expect everyone else to do it your way. Don’t tell us that we need to bow down at the altar of The Book because many of us know better. They’re only as good as what is inside of them.