Another factor to consider is that every one getting infected quickly, and partial herd immunity being established sooner, could expedite the repeal of COVID control measures, and the dissipitation of the climate of fear, which are both incurring significant health, quality of life, and economic costs.
The World Bank estimates that COVID and its associated policies has already pushed 97 million people into extreme poverty. UNICEF says "Schools still closed for nearly 77 million students 18 months into pandemic": https://www.unicef.org/lac/en/press-releases/schools-still-c...
In the US, fentanyl overdoses during the pandemic have surged to become the leading cause of death for the 18 - 45 demographic: https://thenationaldesk.com/news/americas-news-now/fentanyl-...
Scientists have long known that social isolation is deadly, and if there's one thing that COVID control policies increase, it's social isolation.
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[0]: https://www.beckershospitalreview.com/workforce/about-1-in-5...
[1]: https://medicine.yale.edu/news-article/burnout-alcohol-ptsd-...
https://www.theguardian.com/world/2021/nov/23/pandemic-hits-...
Keep in mind, this isn't just 20% fewer people to deal with COVID, it's 20% fewer people to deal with, well, everything, for years to come. I'm sure someone's done the calculations on what the consequences of a decimated healthcare system are, if you want to go look for them.
How much worse do you think everything you've listed would be if we had started with 20% fewer healthcare personnel? Well, guess what. That's how bad it will be from now on, because we couldn't all cooperate to take measures to ensure the healthcare system didn't get overwhelmed in the first place, and doesn't continue to get overwhelmed.
That's why I asked how you could arrive at the converse conclusion that lockdowns are net beneficial for mental health.