Laws against rape and murder facilitate the prosecution of those crimes, but not necessarily the investigation. Furthermore, the trade in child porn is not legally the same as the crime of rape, but does have measurable negative effects.

As for people moving, I certainly can know that if we're talking about existing and imminently foreseeable conditions. That you need to posit a completely alternative reality where the act of communicating is a crime suggests your argument is fundamentally weak. I'm pointing out the demonstrable lack of interest under current and historical conditions. Available evidence suggests that people are pretty attached to places and prefer to undertake clandestine activity rather than just up and go somewhere else short of a stark existential risk.

Do I know this to be true in the epistemological sense, of course not. Am I pretty damn sure about it in an empirical sense, yes I am. I've moved repeatedly and feel little or no emotional attachment to my birth family - in fact the farther away from them the better I like it. But this is really really unusual. the vast majority of people are intensely concerned with maintaining their family ties even at significant economic/political cost. Just because I don't share that mindset doesn't mean I can blind myself to it.