Proposed contact-tracing apps would do a lousy job, because what they try to do is very different from real, effective contact tracing.

Don't assume that a system, once actually in use, will respect any sort of privacy for anyone.

I hope the US does set up effective contact tracing, and if I am ever called because of a rational suspicion that I am infected and asked about my contacts, I will do my best to cooperate. If I am told I am likely to be infected, I will stay inside to protect others. But I will not use something that would let the state track my movements even if I do not become infected. I will not carry a portable phone.

To throw freedom and privacy overboard to avoid a small incremental risk to health is folly. We need to maintain our freedom and privacy along with our health.