If only people did this with care. I have seen too many books where people just highlight everything.
(I do wonder if the people here who hate it are picturing students who blindly highlight pages, and the people who like it are remembering the times they've seen a few pencilled sentences in margins of an old book)
nor was there a reason to blanket discourage treating books as precious and worth preserving. i'm interested in the part where you note what you noted and let the other glaring transgression pass. That was a choice.
Not all books, of course. If you're reading a self help book or some technical one, scribble away at your heart's content.