Crime and Punishment
Because punishing people for a crime committed _against_ them is the most logical way to deal with this.
Let me preface this by mentioning that I am an American. Something like this came up in another forum, but isn't it the case that "In the UK, possession of child porn is a strict liability offence, so it doesn't matter if the host is genuinely unaware, they're still guilty." I would think that fits the punishing the victim model pretty well.
To play the devil's advocate a bit, while licensing seems a bit extreme, we do have laws concerning computer usage. In fact, some aspects of computer usage, equipment, and software are military considerations. It would seem to make sense to at least invest in public education a bit more than I have seen in the US. Public service announcements anyone?