I think a lot of people in this discussion are pitting the argument at people prioritizing their individual choices over the collective health of the community. I think that is a very singular framing from one side. A lot of people I know just believe that the virus itself is not as deadly as the reaction warrants. The infectious mortality rate of Covid is at best twice that of the normal flu, which isn't nothing and…
Discounting externalized costs to zero is rational, true; that's the source of the tragedy of commons (in the economics/game theory sense, not necessarily the somewhat disputed original example for which the effect is named.)
But that's a manner in which individual rationality is insufficient to address issues whose effects aren't limited to the individuals engaging in transactions.