It’s optional and opt-in now. Do you trust it to stay that way once the framework is in 99% of people’s pocket? I sure don’t.
You’re thinking the contact tracing platform somehow paves the way for an actual surveillance system, but it doesn’t. If they want to build a surveillance system then they will, and the success/failure/adoption rate of their contact tracing platform won’t affect that at all.
Building surveillance off the contact-tracing platform would allow the three-letter agencies to track movement of a single device regardless of whether or not you try to sever its connection to the cellular network. You might be able to hide a single device from the network, but would you be able to hide all the other devices around you that are trying to snitch on you?
Surveillance is more than just the technical means of data collection but also the societal framework in which it occurs. Contact tracing, if it worked, would have been a bunch of "good PR" for surveillance in general, and that affects how people will react to similar increases of data collection in the future. How to you think the FBI's 2015 case against Apple would have gone if there was already precedent for unlocking devices if the owner was thought to be infected?
They can do this without the contact tracing platform.
Regarding PR, that too can be done very well without a contact tracing “success story”. Also, forcing people to unlock their devices is not an element of the the contact tracing platform.
I’m not sure why you’re convinced the contact tracing platform is a necessary or even helpful step for any of these things you worry about. But it isn’t. You will be able to take more fruitful actions against these things once you understand that.
This feels like a "slippery slope" argument. If so then I would argue the situation demands us to take a small step further towards the start of the slope.