@marginalgain - define "mild"
How many people become ill enough to require hospital admission - not just ITU but hospital care.
Now what do those figures look like without a lockdown? The NHS couldn't cope with all of those people requiring hospital care at the same time.
How many deaths would you then have from heart attacks, strokes, aneurysms, acute abdomens, fractured hips and pelvises, traffic accidents, falls, illnesses in children? All of the day to day life threatening conditions that the NHS treats would still be happening but while it was overwhelmed by Covid patients.
How would other services cope if large numbers of workers were off sick at the same time so infrastructure collapses? Currently that's being protected by slowing the spread so by engineers are still maintaining phone lines and broadband, electricity and gas supplies are maintained, food is still available. Imagine dealing with this without access to a phone, no power and no food?
But yeah, great idea to let it run wild.