Porn addiction like any other addictions (gambling, sex, drugs and rock and roll, etc.) materializes when it is done on a regular/continuous basis. Our mind will be clouded to the point that our conscious mind will be overcome by our subconscious and could no longer differentiate whether such act is within the ambit of "normal" or not.
I am not against watching porn since it has some positive aspects to it. Those who committed the crime of acts of lasciviousness or even rape are usually those persons who can't control their sexual urges and therefore has a weak mind frame. If the sex urge is apparent, by watching porn and releasing the tension afterwards will tend to shun our mind from committing rape or acts of lasciviousness as it will help you return to your proper senses.