We aren't just shutting everything down to save lives, we're shutting everything down because we some reason to believe that if 70% of the population gets this disease in a very short amount of time 20% of them are hospitalized, and at least 2% die (in truth, the CFR would skyrocket if we don't flatten the curve), the societal and economic havoc would be much worst than the one resulting from these government imposed quarantines. At the highest end of the risk spectrum, it could be orders of magnitude worst. Do we know that for sure? No, hence the Russian roulette analogy: some chance of extremely high risk, esp. when it comes to the entire planet: NOT WORTH GAMBLING.

If you think that world leaders are currently sacrificing the economy just to save lives, you are not paying attention to what they have been doing.

True, this is only in China. In most other countries, it's still too early to be able to collect great data because of how quickly the situation is evolving (the denominator is bound to be wrong due to delays between cases being detected and the amount of days it takes before cases evolve into severe/critical condition or death). But it's data, and you can't easily dismiss it.

> So they are inexperienced experts giving it their best guess based on what they know about disease transmission and math.

This isn't entirely true. The epidemics in China, South Korea have more or less been resolved, and many of the steps being taken in other countries are based on comparing the outcomes in those countries compared to ones that are failing to slow the spread of the disease with disastrous consequences (Italy).

> But they clearly did not factor in the effects of shutting down the global economy for 3-6 months in their quest to optimize for a single variable.

It's possible that the health experts are not taking the economical windfall into account, but the politicians enacting the laws probably are. These decisions are being made in rooms with people who, with their knowledge pooled together, most likely have more information about the disease and the economic impact of their decisions than you.

Secondly, the reasoning for national shutdowns earlier rather than later is to shorten their length. As of now, local government officials are hoping not advocating 3-6 month shut down, but rather trying to avoid one by shutting down now. I remember reading the figure of 2 weeks but I cannot find it quickly now. We will see.