The author does not think it's ridiculous at all. The next paragraph exactly addresses your comment: > If we are only taking into consideration the information

The author does not think it's ridiculous at all. The next paragraph exactly addresses your comment: > If we are only taking into consideration the information that is immediately available then the situation does indeed seem pretty ridiculous. But if we stop and consider what might be the broader context we can imagine scenarios where wearing a mask alone makes a lot of sense.