Finally, researchers are starting to acknowledge that porn IS problematic for up to 60% of users. But they're looking at the "psychological processes," not the "physiological brain chemsitry processes." Psychologists still want to explain it all with "guilt." I'll see if I can get the full study through my library. Here's the abstract.
Published in: Sexual Addiction & Compulsivity, Volume 16, Issue 4 October 2009 , pages 253 - 266
This study investigated the prevalence of problematic Internet pornography viewing, how it is problematic, and the psychological processes that underlie the problem in a sample of 84 college-age males using an anonymous online survey. It was found that approximately 20%-60% of the sample who view pornography find it to be problematic depending on the domain of interest. In this study, the amount of viewing did not predict the level of problems experienced. Mediational analyses suggest that the manner in which an individual interacts with urges to view pornography may be related to whether viewing is problematic or not.