>On the other hand, detecting you really broke an openly-accepted law, triggering police intervention and letting the system work as it should, is trivial in the extreme.
Yes, but on the other hand, speaking of "detecting you really broke an openly-accepted law", China has 1/2 or 1/3 the prison population per citizens that the US has (which is the world leader in this regard, with 25% of the worlds prison population for just 4-5% of its general population).
It's a very different thing, simply because it cannot be deployed on a large scale. It's equivalent to old-school spycraft of honey-trapping and blackmailing. You can apply this process to a few individuals, but not to everyone without massive effort - the framing and follow-up takes too much manpower - and without risking reputation damage from repeated abuses.
On the other hand, detecting you really broke an openly-accepted law, triggering police intervention and letting the system work as it should, is trivial in the extreme.
Sorry, I'm not a fan of the US system but China is still a step below IMHO.