Not at all snarky because I have no idea what the real answer is here, but although this sounds pretty good, it strikes me how in conflict this would be with most peoples' ideals if we tried any sort of system to scale this to larger populations (like a city).
Perhaps we want privacy-but-not-anonymity. Or perhaps society doesn't scale easily.
The real answer is to rebuild the high trust society by relentlessly removing the low trust elements, the same way the high trust society was created to begin with.
That isn't a real answer. There is no effective way to remove the low-trust elements who physically operate in jurisdictions with no effective law enforcement. Like what are we going to do, fire cruise missiles at random Internet cafes in Nigeria and Cambodia?
We are heading for a period of a not-fully-connected internet. Already people are cutting off China and Russia from their sites because their bot traffic is either overwhelming or malignant.
Those are not alternatives. VPNs and botnets already exist. We have minimal practical ability to control Internet traffic or transactions between most foreign countries. All it takes is a single compromised device in the USA for the scam traffic to get through.
Come on, be serious. No one is going to cut any transatlantic cables just to prevent scams. VPNs make a huge difference: as long as you can get a route out somewhere then you can use a VPN (possibly to a compromised host) to make your traffic appear to be coming from another source.
Perhaps we want privacy-but-not-anonymity. Or perhaps society doesn't scale easily.