[CrazyStat]

> specific probability (which would be an oxymoron)

Not at all. For example, if I flip a fair coin, I can assign a very specific probability to the event that I get heads.

> We know it's a couple of orders of magnitude worse than the seasonal flu

Maybe one order of magnitude. Seasonal flu is about 0.1-0.2% mortality in the US. The evidence suggests that covid-19 is less than 1% mortality.

> hence the extreme quarantine measures to reduce its infectivity to essentially 0

It doesn't need a high mortality rate to justify extreme quarantine measures. The fear is that it will become a perpetual thing, another seasonal illness like the flu. Even if the mortality rate were the same as the flu it would be worth taking extreme measures to avoid that.