2. Fame, recognition, i.e. non-monetary benefits to being a good writer.
3. At least some people write because they believe what they have to say is important and/or helpful.
4. People will always want to own physical books. This is different than music or a dvd as a book can be passed-on/gifted much easier than a DVD or a CD, which will be obsolete.
I can see both arguments, but I'm definitely not worried about the possibility that people will stop writing books.