Let me stake out a position here:
I think that most people who are happy to freely duplicate copyrighted works have never been in the position of selling anything of their own.
I think that people who sell their own materials (be it books, music, software etc.) are more likely to be aware of the effort that creators put into their creations. Such people are more likely to identify with fellow creators. They are thus less willing to duplicate material without fair recompense because they know how wretched they feel when they see copies being made of their own materials.
These beliefs lead me to make the following testable proposition: A person who starts selling their own original materials will be less willing to duplicate the copyrighted works of other people.
I welcome informed discussion. Of course, this is Slashdot, so I expect the signal-to-noise ratio to be woeful!