Treating a threat as existential is often enormously costly, and we reliably overestimate threats. Ignoring them is a good first response, if not always a good second one. Being a week or a month late to the current pandemic is less costly than locking down for SARS, mad cow, bird flu, swine flu, ...
Not to mention the times when we did overreact. The latest TSA budget is $8.24 billion dollars, or 824 lives per year (at a cost of $10 million per life), or 2.17 One World Trade Centers per year, or (verging into polemic) one 9/11 every four years.
Isn't the lesson that we tend to overreact? Sure, maybe it'll be a pandemic, and let's not completely discount the idea, but why not just lock the plane's cabin doors and see if it gets worse?