I think part of the problem too is that some of these people might decide to try something small once or twice... Like one small job for a few thousand bucks, etc. But once they've started, it's probably VERY difficult or even downright scary to say "No!" to whoever they're working for.

The reason I say this is I remember a story a few years back about a pilot that was asked to smuggle some pot in a rented plane across the country... He only wanted to do it once, but after he did it he was basically made an offer he couldn't refuse for subsequent trips. I think he worked for a fractional as a captain.