The Sherlock Holmes principle is, once you have ruled out the impossible, the remaining explanation, however unlikely, must be correct.
Applied to the question of what degree of lockdown* to impose, there are two strategies:
1. The Swedish/Brazil "hope for the best" herd immunity strategy - this might or might not have been a good strategy given the lack of clear information at the time**. But it always had a theoretical chance of working and, with the benefit of hindsight, seems to be working, especially if you take into account the economic, social and educational damage that such countries have avoided. This of course involves the elderly and vulnerable voluntarily self-isolating, and it will cost money to employ people to do their shopping etc for them, but that is a small cost compared to the economic etc damage caused by a full lock down.
2. The "suppress infections until a vaccine comes along" strategy which cannot ever work. I can sort of see the point of "flattening the curve" but they've done that. The NHS wasn't swamped and isn't being swamped.
a) Even if they develop a vaccine that works (unlikely) at some point in the future (months? years?), are we all going to take it (no)?
b) If immunity is only a few months after having caught it (the arguments AGAINST the herd immunity strategy), then the same will apply to people who have been vaccinated. So this will require endless repeat vaccinations.
So strategy 2 can only ever be delaying the inevitable and can never succeed.
Ergo, given a choice between a strategy that MIGHT work (and appears to be doing so, with the benefit of hindsight) and one that CAN'T POSSIBLY work, surely you choose the former?
* It is a question of degree. Some things appear to worth trying where the economic cost is minimal, for example banning large gatherings (concerts and football matches); turning down music in pubs; face masks on public transport; encouraging people to work from home. Testing people for coronavirus after they get off an airplane or boat misses the point - it makes more sense to test people before they get on at the other end and to turn away passengers who test positive. Not sure on the logistics of this, but that's the principle.
Things like shutting pubs at ten o'clock are insane. Is the virus more infectious later in the evening? I think not. People under 30 are barely affected, so shutting schools and universities is also insane. The older teachers and lecturers will just have to take a sabbatical.
** The best information we had was the Diamond Princess. That was pretty much a Petri dish. 15% of the 1,045 crew tested positive and precisely none of them died (being presumably young and healthy). Twenty percent (or should I say "only twenty percent"?) of the 2,666 elderly passengers tested positive and twelve had died between the first positive test in early February and the end of March when most lockdowns were imposed (two more died in April).
Scaled up to the UK, we'd expect to see around 50,000 deaths among the elderly in the first two months, which is not far off the actual outcome. To paraphrase Prof Michael Levitt, that was the Grim Reaper taking all the people who would have died during the previous two years' flu seasons, but didn't because they were very mild. A year ago, UK undertakers were worrying about the low number of funerals!