Before the fall of man into sin, public nudity was pure innocence. After the fall, public nudity became obscene. Why the change?
In art, the naked body is celebrated. In pornography, the naked body is demeaned. Why the difference?
Marriage was the first sacrament, and an archetype of all the following sacraments. Fornication, especially adultery, is the chief among earthly sins, and the foundation of a rejection of God, the ultimate sin. Why the contrast?
The answer to these three questions is simple: lust.
Before the fall, man was shameless; that is, he did not know shame. Man and Woman only saw the image of God when they looked at each other's nakedness. Once they ate of the apple, their eyes were open to allow them to see each other as sexual objects (lust). To have someone look at you with lust, would naturally fill you with shame, and you would want to hide your nakedness.
Lust is powerful! One can overcome the shame of being the object of lust, and therefore gain power over the lusting. This is also shamelessness, but now it is disordered. To have someone look at you with lust, should naturally fill you with shame. Abandoning this shame is to abandon the very nature of what it is to be human.
This disordered shamelessness has given rise to pornography. Personally, I find nothing more beautiful and attractive than the naked human body, both male and female. However, at the same time, I find nothing more ugly and repulsive than the naked human body, again, both male and female. The difference between art and pornography is intent. If the intention is lust, it is pornography; otherwise it is art. The screensaver on my compute contains a great deal of nudity, but I am not embarrassed when my children see it. This nudity is in the form of great pieces of art, such as by Alexandré Cabanel, or Michelangelo Buonarroti. However, when I check my spam for legitimate e-mails, I make sure my children are not in the same room.
Intentionally viewing pornography is committing fornication or adultery in the heart, and not much different than acting out this fantasy. Fornication and adultery are the ultimate culmination of lust. It is the denial of what the human body really is: the image of God.
For a man and a woman to really know each other, they must freely give their body and soul, and become one. Anything sexual outside of this self-giving is lust. Within this sexual self-giving, the man and woman are naked with out shame; the shamelessness of innocence. Within lust, the man and woman are naked with out shame; the shamelessness of obscenity. Nudity can be innocent, and it can be obscene. Which do you choose?