My mother lost her mind if anyone cracked the spine of a book, let alone fold down a page edge. My paperbacks have cracked spines, folded down page edges, pieces of envelopes as bookmarks, and sometimes even penciled notes (underlines for favorite quotes, and occasional “!”, and the correction of typos that slipped by the editors.) I can’t imagine throwing any of them away.
I even buy unloved books at garage sales and turn them into art projects rather than see them get tossed.