Here is another consideration: our culture is saturated with pornography chiefly because porn is cheap; hiring a person is considerably more expensive. The costs of porn have reduced dramatically, whereas the costs of tricks steadily increased. In the 17th century, buying porn was economically unsound, because the services of a gutter girl could've been procured for a fraction of the cost of a pornographic print. Sexual frustrations were addressed through ubiquitous prostitution rather than porn. Yet porn had to begin somewhere, and it could've started only in a situation that is opposite to what we are having today.
With these considerations in mind, why was it invented in the first place? Like most of the inventions, pornography aimed at one thing but instead became another, and that is what makes it story interesting and instructive.
First, let me introduce the inventor of porn: Pietro Aretino,
Aretino was a friend of Ariosto, Titian, Raphael, Tintoretto, Romano, and Vasari. Michelangelo used him as a model for St Bartholomew in the Sistine Chapel; Titian painted two portraits of him; Tintoretto famously held him at the dagger point for writing badly about his work.
Inventing porn required a leap of imagination; only a Renaissance would be able to make such a leap.
Apart from his natural libertine inclinations, which he shared with many other men in his circle, Aretino was one of the first authors supporting themselves by writing in vernacular for wide readership, and he quickly discovered that without patronage such writing does not pay the bills. As he was a rather sharp satirist, there was a problem with the patronage. His ingenious solution to his fiscal problems was porn. The difficulty, as was stressed above, was not in producing porn; it was in finding a way of selling it to wide readership, as Renaissance folk did not need porn. Inventing the formula that allowed such a transaction was Aretino's genius.
The story how Aretino invented pornography is told here.
Porn was invented as a means of political/social satire appealing to common people, for the purpose of democratization of humanistic criticism. The first printed erotica was philosophical and cerebral, appealing to Ovid and Lucian, and that made it unsuitable for the masses. Aretino wanted to reach a very wide audience, both to make profit and to impart his critical message. He realized that he can appeal directly to the streets rather than the pagan past. Porn provided the medium for lampooning his fellow humanists as well as the clerics, princes, and anyone else, because showing one's powerful enemies engaging in sex was the surest way to degrade them to the level of common folk. It was his satire that drew people into buying porn; he only needed to make it as salacious as possible for the maximum effect. So he wrote a chat between a prostitute and her young daughter (who is about to enter the trade) about her pretentious clients with their pretentions of virtue; the whore knew better, seeing them for what they were. The narrative was made more engaging by interspersing it with suggestive images showing the vice of these clients. Aretino's success was sensational. For 200 years porn followed his formula without any change.
...In an era when "pornography" was defined as much by the novelty of its message as by its graphic sexual content, Aretino's sonnets and dialogues represented the worst of all possible worlds to the authorities who banned them. By using pornography as a vehicle to attack everything from the humanist educational program to clerical piety to the vicissitudes of court life, Aretino exposed the vices of the upper classes to an indiscriminate readership. He further offended the upper-class sense of propriety by putting his pronouncements in the mouth of a whore. Aretino was more dangerous than all the erotically inclined artists and humanist pornographers put together, not because of his frank portrayals of sexual behavior but because of his refusal to restrict his audience to men of virtue who were allowed to read the erotic classics due to their "eloquence and quality of style." While Aretino's canonical status in the world of post-Renaissance pornography rested on the infamy and rarity of the sixteen modi and the accompanying sonnets, his contemporary reputation was a product of his desire to publicize, and therefore betray, the practices of the courtiers and humanists with whom he was intimately familiar.
...The use of prostitutes in pornographic writings was not an idle choice. They were the embodiment of vice and yet exhibited a certain detachment from the social hierarchies, due to their perceived marginality. It gave them a privileged view of the practices of others and, thus, empowered them to speak, quite literally to "authorize" a portrait of society. Their gaze, however, was not the pornographic one, though they existed to foster it. Instead, it was the critical gaze of the pornographer, who looked into the souls of men and told them what they least wanted to hear. Like Aretino, whores are manipulators of the pornographic gaze. They have the power to move others, but do not succumb to temptation. What does all this have to do with the invention of pornography? The erotic and obscene writings of the sixteenth century set the stage for the more widespread diffusion of pornography in the seventeenth and eighteenth centuries by charting the terrain in which pornography was formulated, and by setting the parameters of its subject and the techniques of presentation. Voyeuristic and subversive, pornography quickly became the preferred medium through which to vent one's outrage about the ills of society while, at the same time, making a tidy profit.
This original intent of Aretino's porn has long been obsolete, but that's how Renaissance public was hooked on his invention. It purpose was no less than preaching the republican virtue to the commoners by means of demostration of the vice of the elites. Aretino sincerely believed that his ridicule would uproot the vice. In reality, his exposition only wetted the appetites of the have-nots. The end result of his campaign for improving public mores is the trailer-park folk grimly watching their Internet porn; these modern have-nots do not have even what the have-nots of Aretino's time had in great supply.
It strikes me that the hatred of the ruling classes invariably produces the same - unmistakably pornographic - gaze, whatever is the motivation for such criticism. I doubt that the depictions of corruption and vice, even if these are offered in good faith, have the intended effect, as they only arouse the meek to new exciting possibilities. The likely result is not the improvement of a human lot but inventing yet another variety of porn...