Re: the masks on planes. Assume a linear rate of virus particle shedding per breath and calculate the total viral load in the air of the plane over time, assuming the mask can catch a resonable proportion.

The "pointless ceremony" of "masks while not eating" works out better.

I think because we see ourselves as "sick or not sick" and "infected or not infected", people are not very calibrated to think or care about magnitude of exposure.

Public health prophylactic measures can have real impact on both large and small scales, even when imperfectly followed. It's the statistics of the thing. Terrorism measures are stil theatre IMHO because they have such a lumpy and weird distribution.