There isn't a data sharing protocol on the Internet that isn't full of "some very foul and probably not entirely legal pictures." You ever hear the tune, We Built This City? Well, in that tune, the city was built on rock and roll. The Internet was built on porn. Plain and simple.
If you were a bbs operator in the eighties and nineties, it didn't take you long to realize that the boards that got the most calls were the boards that offered porn. Hell, even our local Mac Users Group ran a First Class bbs with a special porn section for its adult members.
Ever go to a computer trade show back in the eighties to mid-nineties? Back when distributing public domain and shareware on floppy disks for a fee of between $5.00 and $10.00 per disk was the in thing for computer junkies? The biggest section of their PD & Shareware catalogs were the porn sections.
Back when commercial bbs' were still popular, MacUser and, I believe, MacWorld magazines ran ads for porn systems in the back of their magazines. Porn was just as responsible for the adoption of personal computers by consumers as games were.