Apple and Google, which do enormous amounts of tracking of users, have become the unlikely guardians of people's privacy by limiting how apps can get data about bluetooth contacts.

In addition to blocking various abusive forms of surveillance, they also prevent any sort of contact-tracing app that accumulates a list of phones that have passed nearby, even if it were up to the user to decide to send it in.

If such an automated recording of nearby-passing phones is an effective method of contact tracing — which some experts doubt — then preventing it from being used seems to be a bad thing.

In addition, governments can do this in other ways, as China does. I think China's app operates by reporting the phones GPS location to the state. If everyone is forced to install that app, the state can figure out which phones passed nearby.