I don't understand why at risk people don't just stay at home. Why lock everybody else up? Enough is enough, kids need to go back to school and people need to go back to work. This document seems hand-wavy and doesn't answer anything.
First, because they live with people who aren't at risk and if those people go about their lives it defeats the purpose. Second, if everyone not explicitly at high risk went about their normal business, some percentage of them would still need medical attention and the hospitals would run out of beds, leaving some to die.
Second: That's the nature of nature. If you want, you can protect yourself, stay home!