To sum up the weird way that we all watch a ton of porn but don't talk about it, sex spreads disease and risks childbirth.
Reading doesn't.
Because it is so dangerous it becomes a taboo thing, it can't be public and widespread otherwise it would cause huge damage. So it's kept where it is safe, behind closed doors and between relatively small numbers of individuals that you don't end up with is massive web of connections that links all of society together.