> How many will have long-term pain from learning , nutrition, physical abuse, mental health?
We know that. Not exact numbers, but at least there are rough estimates. It's been an active area of research for quite some time, so there's a lot of data. Statistically speaking, we know how childhood poverty or a missed school year means for average lifespan.
It's been theoreticized that a reason for the differences in pandemic response when it comes to Sweden are down to the fact that they recently unified all their people health issues, that is not only medical issues but also social ones, under one government agency. That broader mandate is generally more data driven and needs to take longer term effects of missing school into account.
> Most policy can be reduced to "Better safe than sorry"
That's not all there is to it. Strictly following that reasoning would emphasize known risks against unknown risks. That does not explain the policy making that dominated during the pandemic.