From looking a bit further, it seems that the publishing industry is very concerned about the availability of free content. This is of course not surprising.
There have been several studies.
Dr. John Hilton's Ph.D. thesis on the effect of free ebooks on the sales of paperbacks.
http://opencontent.org/blog/archives/1313
Brian O'leary's book on the impact of P2P and Free distribution on book sales.
http://www.scribd.com/doc/77102909/I...-on-Book-Sales
Magellan Media presentation on piracy and free books.
https://docs.google.com/viewer?a=v&q...2Mzu2xVp4HQ1IA
I will run the risk of being too broad, but the conclusion of these studies is that the availability of free content boosts sales of paper books. However, they did not find that this was true for every book that they studied. Some books' sales dropped by more than 30 percent as a result of being freely available online. Moreover, some of the studies state that such marketing may not continue to be effective in the future.
I would expect to see that the publishing industry tries to reign in free content. Similar actions have been taken by the movie industry with regard to Netflix and other formerly free providers.
In any case, trying to move back to the original topic, without copyright the publishing industry would lose a great amount of revenue. This would effect authors and result in fewer quality books being produced.