I don't understand your argument. Are you thinking that there will be two kinds kinds of counties at each point in time, those "deemed safe" and those "deemed unsafe"? If so, that would explain my confusion. I imagine that each county would be advised to implement one of a small number of strategies, in consideration of the peculiarities of that county, its economy, its normal levels of travel, its immediate neighbors, and the effect they are likely to have on their state (and even the nation) as a whole.

Are you thinking of the people who would be willing to drive far distances simply to, for example, go out to eat? I would assume that this analysis would be included. Close proximity to a large population that's on lockdown is, in my opinion, a reason to keep the lockdown in a county, even if that county doesn't yet have many cases. But the next county over might or might not open up. Sure, people near the border from the second county will just go into that third county, and that's fine - as long as there aren't too many people coming from the first county.

Politicians and pundits simplify and say stupid things, when taken literally, but when it really comes down to it no one is really suggesting that the state of affairs within a county be the sole determining factor for the degree and form of economic activity which will be permitted. We have to look at the larger region. But once we look at the larger region, it will probably make perfect sense to completely lift the shutdown in some counties (esp. in Alaska, Montana, Wyoming, etc) while keeping a strong shutdown in other places.

Edit: I assume that we will also be looking at individual industries independently. Can the companies in a certain industry in a certain region reliably commit to following strong anti-COVID practices? If so, we might let them open up, while other industries are not allowed to. We don't have the time to create certification bodies or licensing departments to handle these specifics, so politicians will just have to make the best decisions they can.