They'd be subject to background checks and surveillance that they ideally would not even notice - yes, I'm aware that we don't live in an ideal world, but the p

They'd be subject to background checks and surveillance that they ideally would not even notice - yes, I'm aware that we don't live in an ideal world, but the point is that traditional "leg work" policing is pretty good at determining whether a suspect is actually engaged in nefarious activities - but it's expensive and requires a reasonably narrow list of suspects to begin with.