I doubt this is true. There is a readily available technology for beating greylisting for example. Any semi-configured mail server can do it. Yet greylisting al

I doubt this is true. There is a readily available technology for beating greylisting for example. Any semi-configured mail server can do it. Yet greylisting alone stops majority of spam. I expect the same effect for drug or people trafficking. While no barrier will stop everyone, and there are already drones and submarines designed for crossing well-protected borders, even fairly simple obstacles will stop or deter the majority of traffickers.