Three million people dead would monkey wrench the economy no matter what. That more than doubles the number of annual deaths all at once
That's simply not so
The mortality in the United States in 2018 was almost 3M people. So the coronavirus could technically kill as much (if its mortality rate is actually 1%), but we don't know how many people it would kill among those who would still die soon, in a year or two. And as this disease is killing mostly weak and old, the ratio should be high. In other words, it is a complicated matter with a lot of factors largely unknown