[zaroth]

What if the lockdowns just lengthen the duration of the pandemic and the ultimate endpoints are nearly identical?

Some amount of lengthening is essential to keep hospitals from being overwhelmed, of course. In many lockdown environments, the target case numbers are much lower than necessary for that goal, if not zero.

[cookingrobot]

That would be true if there was no vaccine coming and everyone was going to get it eventually. But if we expect a vaccine sometime in the next year or so, we can try to minimize the number of cases and deaths until then. So far about 1.5% of the US has tested positive for it, so maybe 2-10% have been exposed. If we can keep that under 20%, that will be a lot fewer deaths than if we let it run free to herd immunity levels at 95%.

[UncleOxidant]

Exactly. And given that many who have had covid-19 have permanent damage and/or longterm ongoing symptoms it's best to try to minimize the number of people who get it before a vaccine becomes available. A significant number of people with longterm disability caused by covid-19 would also damage the economy.