"In any event, this isn't about enforcing or violating copyrights. This is about resisting the user's efforts to employ their documents in ways which they may well have every legal right to use them. An unobtrusive notice that restrictions were requested might be reasonable, but the purpose of software is to assist users in accomplishing their goals. Any software so perverted as to deliberately hinders its users is an abomination."
Well, what about the goals of the other users - the ones who wrote and distributed the documents? Their goals may well include, for instance, sending documents out for comment or distributing internal corporate documents that they don't want to see copied into rumor-site postings.
Sure, it's not a serious impediment to copying by people who want to do so, but at least you're making sure they know that they're violating the rules governing your distribution of the document. MANY documents are NOT subject to fair use, because they are distributed under other conditions, to which the user has agreed before receiving the document.