I Will Forever Be Writing In My Books - Tumblr Posts
Obviously you shouldn't write in library books or books that you otherwise don't own, but I never understood the "oh my god, don't write in, highlight, fold, or dog-ear any pages in your books, ever, or you're defacing them" mindset.
One of my favorite things in the world is borrowing paperbacks from my wife's collection and seeing all her little annotations. Notes in the margins of used university textbooks have helped me understand complex passages, and given me a connection to students struggling to understand the same things I did. Highlights in novels from the used bookstore have made me stop and really appreciate a passage I might have otherwise glossed right over. Marginalia and annotations in historical texts are a goldmine of information and humanity.
What people prefer for their personal collection is totally valid, but I hate how writing in books gets treated like inherent vandalism. It's just another one of those ways the physical paper of the book gets held as more sacred than the information and the connections made with the book's contents.