“Can’t we just isolate the old and the vulnerable, while the rest of the country goes about its business?” Megan McArdle notes that people often ask that question, but haven’t really thought through what it would look like in a country where 21 percent of those older than 65 live in a multigenerational household. “[A]s soon as you try to figure out exactly how it would work, you quickly see that it is actually a remarkably efficient way to kill an unthinkable number of people.”