That's exactly what I mean. There is no scenario where that is the case. If your numbers tell you that, your numbers are wrong.
The actions are the same regardless: shut down everything except essential services, isolate everyone as much as possible, throw as many resources as possible at your health service. Even then, they will be overwhelmed at some point.
What numbers exactly would lead you to a different course of action, based on what we have already observed?
And, again, that's my point: you're asking why it can't be a ridiculously small number when it should be obvious from the reality of the situation that it isn't!
Second, and that's my point: you can have the same result with two very different scenarios: either a lot of people have/had it but in the vast majority of the cases it goes without symptoms at all. So when a big part of the population gets infected only then you start noticing "ICUs being overwhelmed". The second scenario is: it causes serious problems for a substantial part of the infected so even the small number of those who got the virus will flood the hospitals.
And those two scenarios require different responses.
https://www.eurosurveillance.org/content/10.2807/1560-7917.E...
And the percentage of really asymptotic cases is much lower than the most here expect.
All the tests in all the countries could be seen as the statistical sampling. The speed of the transmission is also known, and surely not fundamentally different than the speed of people needing hospital or dying -- the doubling time is nowhere faster than 2 days, and the typical is 3 days.
In short, it can't be expected that "already everybody has it" in the positive sense of "nothing will happen."
So the true numbers are definitely higher than 0.0005%.
Not everywhere ICUS are being overloaded and morgues are overwhelmed with the dead. And ignorance was the first reason why it happened where that's the case. So anything that could decrease the ignorance should be met with open arms.