It doesn't seem like there really are unknown unknowns in this case though. You can just fix all your non-quantifiable assumptions at current levels, and set so

It doesn't seem like there really are unknown unknowns in this case though. You can just fix all your non-quantifiable assumptions at current levels, and set some numbers for the quantifiable ones. The problem is that any numbers you set that way either involve many deaths, or many months of lockdown, so no politician wants to say them out loud.