"research suggests that people who are infected with SARS-CoV-2, the virus that causes COVID-19, are at their most contagious in the 24 to 48 hours before they experience symptoms." [1]
[1] https://medical.mit.edu/covid-19-updates/2020/10/exposed-to-...
The World Bank estimates 150 million will be pushed into extreme poverty due to COVID-related lockdowns:
https://www.worldbank.org/en/news/press-release/2020/10/07/c...
Education has also been severely disrupted:
https://www.unicef.org/press-releases/children-cannot-afford...
Your suggestion that you can safely just quarantine and not be a risk to others is flat out wrong because you are at your most contagious 24-48 hours before you have symptoms.
Also you may not have immunity after you sheltered and recovered.
I'll agree with you that the response was pretty terrible though.
The links I provided give some indication of the poverty and educational disruption this causes, but unfortunately it's hard for people to admit that mass-quarantines were and continue to be wrong, because this issue has been politicized.
Maybe you're right, and quarantine after contraction of illness was not a fully effective method of transmission control, but just the elderly isolating, instead of every one, was, and is a much more proportionate and sensible way to deal with a pandemic that only the elderly are highly vulnerable to.
This seems to be a big part of your reasoning but I don't think this is true. Yes, risk does skew there. But there are large numbers of non-elderly people who have been severely affected.