Is the existence of a log that you came close to someone you probably don't know to be potentially used for a critical public health purpose, for a limited time, any issue?
If feels like refusing to tell your blood type when you're having a massive hemorrhage in order to "protect your privacy"...
Yeah, the government knowing who was close to whom for how long on a whole-population scale is a huge issue. I personally wouldn't mind if there wasn't an alternative that preserves privacy and is just as effective.
Well it isn't a huge issue (let's be honest, they don't care much, and it's hard to imagine why they would care), and it is actually a once-in-a-lifetime opportunity to see the actual spread of a virus in real time, which would keep researchers busy for years.
This shows the limit of individualism, the belief that I am all (this is what the privacy issue is about). An epidemic is when the group must prevail over the individual and cultures that are more group-orientated react much more effectively (China/Taiwan, Korea).
It is a huge issue, there have been plenty regimes that practically wished for this type of technology. What if Nazi Germany had access to all this tech? Perhaps this is a stereotypical example, I would agree, but what makes you so confident there will never be bad actors to abuse systems we put up?
You don't fail to see how it would keep researchers busy for years, but why would only researchers be interested?
Collective benefit over individual rights is not a novel discussion. I see people trying to make a case for individual rights be construed as anti-collective benefit. These people however are also just people, trying to speak for what they think is right, but often times get criticized for it. A lot of times people consider starkly different cost-balance calculations and arrive at different conclusions but this is rarely made explicit. What if you set the time scale a little differently? Corona might be ravaging the world today, but how about in 50 years? 15? Laws to combat terrorism passed during times of crisis that were supposed to be temporary are still here (not a US resident, I might be misinformed, but I hope my point is evident).
Thus, it's like for a lockdown, it cannot be opt-in to be effective unless they bet on the vast majority of the population to weigh the pros and cons.