Good article: The Porn Myth. The article looks at how porn is unhealthy not for moral or spiritual reasons, but for social and emotional ones.

After all, pornography works in the most basic of ways on the brain: It is Pavlovian. An orgasm is one of the biggest reinforcers imaginable. If you associate orgasm with your wife, a kiss, a scent, a body, that is what, over time, will turn you on; if you open your focus to an endless stream of ever-more-transgressive images of cybersex slaves, that is what it will take to turn you on. The ubiquity of sexual images does not free eros but dilutes it.