There's so much uncertainty that I think it's hard to criticize countries. People were spooked by the Italy situation. I think it's pretty clear that without a lockdown we would have had such a situation in NY and NJ. Hence I believe they really had to do a lockdown.
If Sweden thinks they can get enough distancing from voluntary action to keep numbers within what they can handle, it's hard to prove that they're wrong. But their weekly deaths are pretty clearly growing. I think there's a reasonable chance they won't be able continue their current path.
I feel the same about states in the US with low numbers of cases and deaths. I think they'll get into trouble, but there's certainly no way to prove it.
The danger is that by the time you see cases growing, and particularly deaths, the growth has been happening for several weeks. If you find you're wrong and have to tighten up, it will take several weeks before it has any effect, and likely more than a month to reverse a serious problem. That would argue for opening slowly and waiting a few weeks before the next step.
This would sound more reasonable to make blanket statements like "it's hard to prove that they're wrong." and "there's certainly no way to prove it." if we
didn't have the math understanding and the data, and see for this virus over and over consistently in nation after nation follows the virus math of spread follows in a clear, straightforward way depending on social distancing, that's actually very well understood by epidemiologists, who have explained it over and over to us.
Just over and over, all of these. If I'd not learned from those knowledgeable people who's job it is to understand this, then it would have taken longer to see the pattern, but still, the patter is very clear in the data, such as from here:
Coronavirus Update (Live): 2,637,673 Cases and 184,217 Deaths from COVID-19 Virus Pandemic - Worldometer
So, see, like algebra or calculus, it
isn't hard to understand once you listen to a good teacher about it.
So, the idea ""there's certainly no way to prove it" won't hold up well, if the standard is which nations turn out to have had less deaths as a % of their population say after 2 full years of this have passed. It will be quite clear, and we already clearly can see what matters and how the trend works.