This isn't quite right. The law doesn't stop you from selling a book where you have written in the margins, you just can't make and distrubute additional copies

This isn't quite right. The law doesn't stop you from selling a book where you have written in the margins, you just can't make and distrubute additional copies of the the new combined work. Though perhaps you could buy books to annotate in bulk and then distribute those legitimat but annotated copies. Actually, that is a decent metaphor for what an ad blocker is doing.