This situation with the Diamond Princess has been a comedy (tradegy that is) of errors.

Haha - I thought the Japanese were meant to be an organized bunch - but what you described sounds very 'luan-chi-ba-zao'. Also since read that at least one person who was released having tested negative has since tested positive - which is what you predicted.

At some point, the economic and social costs are going to outweigh the health risks. What is that point? That's the question that intrigues me.

The economic/social threshold is an interesting one. Hard to see how a global economy can soldier on when large sectors of it are increasingly going into shut-down. My guess is if it doesn't tail off with the coming of spring then we'll start hearing a new narrative about 'living with the virus'.