I think you're assuming people saying "jail" is for porn, but most likely the jail is for "piracy".
Yeah, there's more to the internet than just porn related things.
Piracy, drugs, alcohol, treason, terrorism, hate speech, bullying, falsely appearing as someone else, cyber crimes and a bunch of other things that don't necessarily clash against the law but would be horribly immoral especially when compared to modern standards.
By the way, what comes to piracy versus porn, I'd say people who'd go to jail for piracy would go because they have illegally downloaded so much porn