1. When we put in these lockdown measures, we basically had very little science behind the disease. Not locking down and hoping things generalize from very small sample sized studies coming out of Italy (which did enter lockdown at that point) is not prudent policy.
2. The only clean room evidence we have even now is the US Naval carrier that was exposed to COVID. It turned out that amongst those infected, 30% of the sailors were just asymptomatic. Previous modeling assumptions that US policy is driven off of were using 15-20% are asymptomatic. Okay, fine our initial assumptions were off a little, but not orders of magnitude off.
3. The other problem with the Swedish approach is that you can't simply isolate old people in isolation from younger people - healthcare workers, nursing home workers etc. are all fairly young and can be asymptomatic COVID carriers.
4. Even if the mortality for younger folks is ~0.1% the toll that COVID is taking on the lungs of even recovered patients is pretty brutal (anecdotal evidence, needs more study). Especially, if you're an athlete or want 100% lung capacity for the rest of your life, it's a bit iffy at this point if you'll actually get it. It also looks like it's hitting multiple organs and not just lungs, again we don't have much science here at this point.
5. I was hoping we could do antibody testing as a way to judge who can safely go out, but I was watching a Bill Gates interview yesterday and it looks like the testing is not good enough yet to make that call - it still has too high a false positive rate, people with antibodies still can get reinfected if their viral load the first time was enough to only trigger a mild infection.