I think we should break down this topic further. One of the key contention points is whether one respects the book/author by keeping the book pristine vs marki

I think we should break down this topic further. One of the key contention points is whether one respects the book/author by keeping the book pristine vs marking it (or whether the book as a physical object deserves respect). This is purely subjective, and has a historical precedent. Books used to be freaking expensive, so of course you would want to preserve it. Now, most books can be printed cheaply, but some people still like to keep their possessions clean. There are many other examples of this divide, like how people use their tools, pots, kitchens, cars, laptops, etc. The other is whether actively engaging with the book helps with understanding and recall. I don't think there is much disagreement on this point, but this does not require marking the physical book. You can use post-it notes and such, but in the digital age, arguably marking a physical book is inferior to annotating a digital copy and cross-hyperlinking it with other books and your personal knowledge base. Unfortunately both the technology and copyright law is lacking in this area as far as I'm aware, but rather than debating whether to write in physical books, I think everyone would benefit from innovating on the digital side of things.