But since that's not feasible, the alternative is to test as early as possible and hard-quarantine immediately -- by testing everyone constantly and everywhere, for which you really need sufficiently real-time results.
Right now, with soft-quarantine,the virus is still spreading, and the timer refreshing -- as soon as people are out and about again, rates will spike up again. Soft-quarantine is a delaying tactic (smoothening the curve), but not a solution.
But we also can't soft-quarantine for that long, because it's crushing the economy. If we keep doing it, there won't be much to go back to.
You need a test, and a fast one, or you don't have much
Some people, grocery store workers and emergency workers are expected to be working. If you could test such workers as they show up at work, these work places would be much safer.
The "shelter in place" order is pretty as leaky as a sieve to be honest - people are still buying groceries at crowded stores because they don't have a choice. So yeah, if you could really confine everyone for three weeks, the problem would go away quicker but now, when that's not really what's happening, tests as a tool seem useful.
From what I understand it’s the asymptomatic cases that are the problem, and they’re not getting tested anyway.
When you have a ten minute test, why not test asymptomatic people?
Plus also, we need to be working hard now so we have testing, contract tracing and quarantine method available later, when they are need to "mop up" the remaining cases.
If we had widely available, quick, accurate testing then maybe we wouldn't need everyone to be isolating no matter what. Perhaps we still would need to for a few weeks, but not for months which would be a significant improvement.
With fast testing you can control a pandemic BEFORE it gets out of control, like South Koread did. You control every single passenger an the border, at airports, so it does not spread to general population.
If there is someone who is not detected, when you do you control the people in their environment.
Making millions of people stay at home is a FAILURE of the system. You should control hundreds or thousands, not millions.
Testing helps us see the problem and deal with it before we step in it and spread it around.
Isolating is like putting the roomba on a shelf for a while. Without taking that step, no amount of turning on the lights will save you.
Both strategies are important and complementary.
I'll admit that this is a hard one to explain; I've gone through a bunch of drafts for this comment.
There is a 3-5 week (1-2 weeks incubation, 1-3 weeks to resolve the symptoms) lag between infection and conclusion of the disease. So all the statistical information available to the people responding to an outbreak is weeks out of date.
They (government bodies coordinating the response) don't have a snowball's chance in hell of getting ahead of an exponential process with a doubling time of ~4 days if they only have 3-5 week old information. They need sub-24 hour feedback on what is going on. Once that is in place, targeted & proactive methods can be deployed that are less crippling than turning off entire cities.