Here's a back-of-the-envelope calculation to show it's not a purely theoretical concern. Today there was ~25k new cases in the US. If you only detect 1/10, the real # is ~250k. If for each you trace 20 contacts, that's ~5 million ppl minus the overlap you have to test every day.

Again, I have no idea how many people you'd actually have to test every day, but it could easily add up very quickly. It seems to me that, if only for planning, we need to estimate this, but I don't see anyone trying. Repeating "test and trace" like a mantra is not enough.

Here is a website @Roflsaurus16 just told me about. It says that we need to scale up the number of workers doing contact tracing. In theory, it makes sense, but how realistic is this if you'd need to trace 2.5 million people a day or whatever? https://testandtrace.com 

All I'm saying is that, if you're advocating the "test and trace" strategy, you can't just say very general things like that. You have to go into the details of how it would be implemented in practice and show that it can realistically be done, because it's not obvious.