Masturbating, and liking sex, too. It's wired deeply into our brains, Ken. Postmodern cultural theorists' game of sophomorically pinning ill-fitting prolix little sticky-note concepts on reality is fine and wonderful for them, but sex and porno and symbol making are as old as homo sapiens. Fucking is fun. Using symbols to remember that is fun, too, sometimes.
Meanwhile, what does "is the advent of porn linked to modern notions of political economy (public and private sphere)" even mean? Are you trying to say the money economy stimulates production and distribution of porn? Heck, yeah, it does, but who doesn't know that? Are you trying to suggest there was no private life before capitalism? Peasants had huts and hiding places, didn't they? The word "fornication" wasn't coined in 1848...