Ok, I'll bite...
I think you make a good argument. But I don't wholly agree with your conclusion that the desire to watch porn comes necessarily from unfulfilled needs in one's real life.
I think the attraction to pornography and sexually graphic material often comes from the need to play out fantasies that one wouldn't actually want to play out in reality. Not because they're too timid or don't "have the balls"... but for the simple reason that in the real world, actions have consequences. Even if the only consequence is another person knowing.
Many men enjoy watching bukkake videos, but that doesn't necessarily mean they want to stand in a room with 70 other naked men and jackoff on a stranger's face. Similarly many people enjoy simulated rape videos ( and rape fantasies are relatively common... among men AND women ), but again that doesn't mean that any of these people would actually commit such a cruel and violent act. Rather, in both these cases, the image on the screen allows the viewer to do something that would otherwise be impossible. That is to enjoy the elation of actions without realworld consequences.
Obviously that wouldn't apply in every case. But I believe that many times, porn's disconnect from reality that allows the viewer to be a ghost... totally free to indulge their darkest fantasies without fear or self-consciousness... provides a certain pleasure that isn't always fulfilled by sexual intercourse.
In other words, I don't think that porn and masturbation should be viewed as just a poor substitute for sex, but rather as an enjoyable compliment to a vital, healthy sex life.