Should e-Books Be Copy Protected?

"My publisher, O'Reilly, decided to try an experiment, offering one of my Windows books for sale as an unprotected PDF file. After a year, we could compare the results with the previous year's sales. The results? It was true. The thing was pirated to the skies. It's all over the Web now, ridiculously easy to download without paying. The crazy thing was, sales of the book did not fall. In fact, sales rose slightly during that year...."