The point being generally no-one knows if they're positive or not.
The initial "masks don't help" was about protection from getting the virus. Still correct.
Except, the reason masks are useful is stopping the unknowingly infected from spreading it.
Those who have tested positive aren't in the community.
If everyone assumes they might have the virus and acts accordingly you can have a functional society without lockdown.
In fact with that attitude shift alone the resultant infection and death rates are less than Influenza which has vaccines AND appropriate treatments.