1) Neither is wearing pants or a shirt. 2) Something being 'natural' doesn't make it right.
>Assuming that obscuring the face has zero cost is clearly wrong.
It doesn't need to have zero cost in order to be the correct thing to do. The question is whether or not the trade-off is worthwhile. Let's saying masking always under all conditions is too much of an imposition, are there restrictions we can place that make the trade-off better?
For instance: Is masking in high density communal areas during respiratory disease seasons with an X drop in disease propagation worth not seeing people's faces in that setting for that time period.
To extrapolate this back to the pants/shirt distinction; human life would end in a generation if we weren't ever able to take off our pants and shirt as we would never have sex again, but the intolerability of that restriction doesn't make it socially accepted for me to rub my bare ass onto a bus seat.
We can't have a discussion about how best to adopt masks, pants, or shirts as a technology if the only way they'll be accepted is if they're always a pure benefit in any situation.