You point is well-taken, but the assumption that masks are useless or dangerous until proven otherwise is simply the well-established precautionary principle.

You point is well-taken, but the assumption that masks are useless or dangerous until proven otherwise is simply the well-established precautionary principle. Why dangerous? I travel on the London underground regularly, masks are mandatory but that is not universally observed; a large number of those with masks are constantly adjusting them, touching their faces, then touching the seats and the hand-rails. Those without generally don't touch their faces. Which behaviour is more harmful? I don't know, and until we get some hard numbers of the actual effects of real people's behaviour (rather than hamster-in-a-box studies), nor does anyone else.