So, I would think that the _backward_ tracing is exactly what isn't useful when the virus is widespread. What the nice guy I talked to seemed most interested in was figuring out who I had been in contact with and making sure that they were notified and that they isolated until they were certain they were safe. And that seems like a useful tool in preventing spread.

I'm just confused by what you've said. Can you explain or give me cites? Because it seems like the opposite is true, but perhaps I am misunderstanding something.