Benjamin Franklin was a subtly clever, witty, person. He would certainly NOT approve of pornography. It would be too raw, vulgar and in your face for him.
That should be beautiful women.
The Hell-Fire Club was sort of a cross between the Dead Poets Society and a risque Playboy club. John Montagu (Lord Sandwich) was a principal, and apparently Lady Mary Wortley Montagu attended. Although Benjamin Franklin (Agent for a number of American colonies) was a member (although there is no written proof), I have no idea if Edward Montague (the Virginia Agent and a colleague of Franklin's) was involved...
The club formally styled itself the Monks of Medmenham, and originally occupied the caves beneath the ancient Abbey of Medmenham. Its members could reach the Abbey by boat from the river at night and thus not be bothered by `paparazzi'.
Franklin's exposure to the club is described as follows by Cecil B. Currey, in Road to Revolution, Benjamin Franklin in England, 1765-1775:
"... Franklin knew Le Despencer very well. He was fully aware of an enterprise which the Englishman had been conducting for some years more or less surreptitiously, known as the Hell Fire Club. Its activities were familiar to Franklin and he occasionally joined in them...
In his youth, Le Despencer had been a member of ... rakes' groups. In later years, ... he determined to form a secret society that would express his interest in architecture, literature, and religion. Only the cleverest and most humorous of his friends would be asked to join. ...
The perfect location for such a society was soon found. Only six miles from the baron's estate, on the bank of the Thames River near Marlow in Buckinhamshire, lay the ruins of Medmenham Abbey. It had been founded by Cistercian monks in 1145. The abbey was well located in a grove of trees which nearly concealed it from view. The nearest road was some distance away, but members would be able to approach it easily in private boats... and ... could return to their homes in complete privacy. ... Workmen were sent in and the abbey was rebuilt and the grounds landscaped ... to make them into a `garden of lust.'
Marble pillars were erected on which were carved pornographic inscriptions in bastard, or `macaroni' Latin. Small Grecian-styled temples were put up here and there. The groves were filled with statuary in indecent poses. ... Hollowed from a hill was the Cave of Trophonius. A fresco within it pictured sexually robust animals, a crowing cock, and a laughing nun...
The buildings were designed also to carry out the theme of sexuality. ... To one side of the main door sat a statue of Harpocrates, the god of silence... Opposite was ... Volupian Angerone, goddess of secret passion.
Rooms adjacent to the chapel were designed to heighten the sexual utility of the place. There was a Roman Room, its wall hung with paintings copied from ancient and indecent Roman frescoes. Also on the walls were paintings of famous English prostitutes... Small statues of Egyptian gods and goddesses sat in niches in the walls.
The abbey's library was situated near the Roman Room. It supposedly contained one of the most complete collections of pornography in England...
Somewhere between 1752 and 1755, Dashwood ... opened his society, known as the Medmenham Monks, and later referred to as the Hell Fire Club. For his monks there was to be a goodly number of nuns... - the main reason many belonged to the club. Most were prostitutes... some were local girls wanting excitement, but many were ladies of society. Of the last group, one of the best known was Lady Mary Wortley Montagu. Many nuns were wives, mothers, sisters, or the betrothed of members...
The members, or monks, were `dabblers in art and literature', and many were among the most prominent men in the kingdom. There were two orders of monks; the superior and the inferior - twelve superiors and perhaps as many as forty to fifty inferior members. ...
... superior members included ... Lord Sandwich...
A group with a membership of this scope ... could wield tremendous power should they wish to act in unison for political ends. It was for this reason that Benjamin Franklin became a monk ... sometime after his arrival in England in 1764. ... Sir Francis had a huge and elaborate cave dug in the side of a hill on his grounds. It was in this underground headquarters that the monks met after 1762. ...
... Franklin wrote...: 'The exquisite sense of classical design, charmingly reproduced... whimsical and puzzling as it may be in its imagery, is as evident below the earth as above it.' ... Others known to be present at the time were Lady Mary Wortley Montague, and the household of Frederick, Prince of Wales. ..." (Currey)
A number of Franklin's biographies mention the Hell Fire club:
"Franklin enjoyed the seasoned old sinner, who enjoyed Franklin, and they spent parts of three summers together at Wycombe. Le Despencer, once a blasphemer, had recently undertaken a deistic revision of the Prayer Book. Occupied with the Liturgy, he asked Franklin to help him `by taking the rest of the book, viz., the Catechism and the reading and the singing of the Psalms. These,' Franklin later remembered, `I abridged by retaining of the Catechism only the two questions: "What is your duty to God?" "What is your duty to your neighbour?" with answers.'" (Van Doren)
Well, there's more, but I'm more-or-less trying to keep this PG, so if you're interested you'll have to look it up yourself!