If you want the whole country to get herd immunity you will probably see similar mortality rates across the country. 0.3% of the US population is 1 million people. How have the models been proven to be "pessimistic by orders of magnitude?
More importantly, herd immunity is the ONLY solution on the table right now, the lockdown is not about stopping the virus in its tracks. It is about spreading it out over a period of time.
It's unclear what the lockdown is about at all since the government messaging has been incoherent. Many countries have (so far) succesfully contained the virus without herd immunity through contact tracing, and the US government has been making vague comments about pursuing something along those lines despite not doing anything to increase testing volumes to the levels necessary for contact tracing.
Without a lockdown, a month more of infections would have likely bumped NYC to achieving herd immunity, or 60-ish percent, since 20% to 60% does not take long with exponential growth.
This means two things. One, it would mean that we would have almost certainly overwhelmed the hospitals with triple the rate of infections. We've be leaving people dead in the streets and it would be a humanitarian disaster as every hospital was at double capacity.
It would also have meant that the curve would be flattened for good.
I have yet to see any evidence that covid antibodies provide long-term immunity. We can't say with any certainty that the curve would be permanently flattened. It may just be flattened for a few weeks, a few months, or a few years.
I guess Sweden is the counter-counter example. I think the US would have needed to have built out a far different medical system to achieve what they have.
For a few days at the end of March and beginning of April, the hospitals came so, so close to collapsing. Just a few more days up the curve and we would have run out of beds. (In reality, we did run out of beds, as you can see stories of many turned away from hospitals in those dark days, but it wasn't quite a systematic collapse).
All of this happened, we were here to record it. Models are models, and we're in the early days of a deadly, virulent, confusing pandemic. But there is no doubt that our reactions and solidarity saved lives. The imperfect models helped us get there.
Now, there is a more reasonable question of where do we go from here. For urban metropolis like NYC, I think a slow re-open like Germany. We slightly open the spigit so that 20% becomes 40% becomes 60% (and hopefully immunity is immunity) and we achieve herd protection (at great cost).
And likely the less dense, the slower we'll need to go (depending on hospital saturation).
I certainly will cheer the scientists who took the best information they had at the time and worked with the leaders to make the best decisions they could. Yes, I will indeed hold them "accountable".
Oh, wait.
I think the lost life-years of economic hardship could easily outweigh the lost life-years of Covid deaths. That is because economic hardship affects younger people, while Covid deaths primarily affect people with not many years left to live. But there are many other external costs (social costs if your grandma dies) and economic benefits to deaths (lower pension payments, home availability?).
However, given current information, a lockdown for weeks to months seems to make sense, since the consensus is that economic collapse is not yet immanent, and that steps can be taken to help keep the economy spinning when lockdown restrictions start to be relaxed.
At this point, I'm not convinced in either direction.