It is simply not a tenable policy to oppose pandemic lockdowns on the premise that COVID-19 only negatively affects a certain portion of the population. First, the fact that COVID-19 disproportionately killed the elderly was not something that was readily apparent right out of the box, when the virus was spreading rapidly. Hindsight is 20-20. Second, focusing solely on mortality is short-sighted given that approximately one-third of all people who get over COVID-19 suffer "long haul" symptoms that persist for months and may even be permanent in some. We cannot simply claim that the non-elderly have no reason to fear COVID-19.

So far, COVID-19 has killed more Americans than we lost in World War II, and it took the war five years to do what the virus did in one year. Even though the majority of the deaths were 65+, these are staggering numbers. Losing well over 100,000 people under the age of 65 in one year alone is nothing to sneeze at, and that's with lock-downs and other harsh measures being taken. A "let them live their lives" approach would doubtlessly have escalated those numbers greatly.

The best early policy for any pandemic is to ramp up rapid testing as fast as possible, and test people constantly. A widespread testing regime (like in South Korea) would allow uninfected people to live more or less normally, while stifling the spread of the virus by identifying infected people quickly so they can immediately quarantine and prevent further spread. [Alex's] earlier post on Testing and the NFL is instructive on that point. Such a testing regime could have enabled us to avoid harsher measures later on. But, unfortunately, America was led at the time by a president who did not prioritize testing (and in fact discouraged it to hide the spread of the virus) and sought to pooh-pooh its danger, shrugging off even the slightest mitigation efforts, like masks. Even after he got it, and was hospitalized, almost put on a ventilator, he acted as though it was nothing. That leadership caused a dangerous cognitive dissonance in public perceptions of COVID-19 -- a dissonance that is causing people to take unreasonable risks, refuse to get vaccinated, and otherwise take actions that will make it even harder for us to get out from under this pandemic.

Focusing on the Great Barrington Declaration itself, the big problem with its approach is that it presumes that "herd immunity" will naturally occur with COVID-19 at some point. The evidence indicates, however, that natural infection does not lead to permanent immunity. The worse a person's symptoms from COVID-19, the longer their immunity lasts, but that's it. The only immunity that is possible now is through vaccination, and even that will require yearly updates as the virus mutates as it is already doing. Eventually we will have it under control. But the suggestion that people under 65 can just safely infect themselves into herd immunity is likely an impossibility, and certainly not a good enough foundation to rest any pandemic policy on. https://www.nature.com/articles/d41586-021-00728-2

None of this is meant to minimize or challenge the obvious economic and mental health effects of certain pandemic policies. There are a great many costs being imposed by lock-downs and other policies. Businesses are failing and not coming back, jobs are being permanently lost, people are feeling isolated, on and on. All of that is tragic, and could have been largely avoided had we aggressively pursued testing (especially rapid-result testing) from the outset. When the next pandemic comes, I hope our descendants remember that lesson. Because once the pandemic started spreading because we didn't get a testing regime in place, it was too late, and then the harsher policies became inevitable. The horse was out of the barn, and the game changed for good.

That is from James N. Markels, responding to Don Boudreaux in these comments.

Here is another way to put the broader argument, not my preferred first-order response, but I think significant nonetheless.  Given the way government and public choice work, anything that kills over half a million Americans is going to be a big deal for policy, whether we like it or not (Don should be the first to recognize that government will restrict your liberties for far less than 500k deaths!).  You want the best feasible version of a response, as there isn't really a stable libertarian response pattern out there.  Trying partial but non-sustainable libertarian approaches will in the end get you more and more statism as the virus keeps on defeating you, deaths rise, and calls for ever-greater state action increase.  A lot of what libertarians don't like about lockdowns in part stems from the "do nothing" response of the first two months of notice that we Americans had when Covid first appeared in China.