> But if the allowable uses and time-frame were set into law
They were with the Patriot Act, though. And many of its provisions are still being routinely extended.
The problem is that once all this data starts flowing in, government agencies who want to use it will find loopholes to apply it in scenarios it wasn't intended to be used, but which the law didn't anticipate. And then, once it proves useful for something important, they'll point at it as the evidence that it's too useful to allow to expire. Again, we've seen that with Patriot Act - originally passed solely to "combat terrorism", DoJ is now justifying their asks for extensions by, among other things, the need to fight child porn. Which means that any politician who votes to not extend it, risks being painted by their opponents as aiding and abetting sexual predators.
This has all the potential to be an order of magnitude worse. A real-time location database for practically every person in US would get all law enforcement agencies salivating immediately. And worse yet, it will actually let them solve otherwise unsolvable crimes etc, and set up a showcase. Probably terrorism and/or child porn again, because it pushes so many emotional buttons at once. And who would dare say that it's not justifiable, because child porn is less of an issue than coronavirus? More importantly, who would get elected after saying that?
That's the real danger of creeping police state - it works more or less as advertised, and it's just too easy to ignore all the "abstract" stuff about freedom and privacy (until you're its target - but most people don't expect to be one, and most of them won't be). So every inch that it gets is nearly impossible to wrestle back.