>As in: The CDC is a huge government bureaucracy that employs (and cannot swiftly fire) enormous numbers of people from diverse backgrounds. If RCTs aren't the standard, well then why not also wear crystals to ward off the virus? They're inexpensive, and they couldn't hurt-- you can probably find a poorly controlled study to support it too.

Alexander's discussion of parachutes gave some good heuristics for when you should trust common sense vs require an RCT, which explains why his advice doesn't generalize to advocating crystals.

The heuristic was basically that you should trust common sense when

a) there's a solid scientific model of the key dynamics,

b) the purported remedy is cheap, and

c) the costs of not stopping the threat are disproportionately high.

Crystals meet b)[1] and c) but fail a) -- we don't have a validated model of crytal/virus interactions. In contrast, we know that (some) viruses (including this one) spread through unimpeded airflow, and masks impede said airflow. We know that high-speed impacts between your body and the ground are deadly, and parachutes demonstrably slow the falling speed of objects.

Thus, you should go with common sense in the absence of an RCT for parachutes and masks but not crystals.

[1] They might fail b) depending on the particular charlatan!