When enough people feel that it’s OK to do a thing, that thing ceases to be wrong in their own cultural context. You can complain about moral relativism all you like, but the facts are inescapable: that’s how people behave. When the photocopier came along, people simply didn’t think it was wrong to copy a few pages out of a book, even though it was against the law and the authors would have preferred that they buy the whole book. So eventually, the Fair Use doctrine evolved with respect to copyright materials. The law changed. It’s now OK to photocopy parts of books for educational, non-commercial use. In effect, the authors and book publishers had to give some ground in the face of the overwhelming tide of public opinion.