Sure, science progresses over time. It's fallacious to say that science is wrong because we used to think the sun revolved around the earth. Evidence evolved, ideas changed.
But dismissing all instances of scientists changing their mind, when they really just lied, as "oh, evidence evolved" is the kind of thing that (I feel) erodes trust in science.
I think the evidence is strong that advice against masks was a lie meant to prevent panic, not honestly communicated "best we could do at the time" science. A lie with good intent for overall public health, but dishonest nonetheless.
"For respiratory exhalation flows, the critical size of large droplets was also between 60 and 100 μm, depending on the exhalation air velocity and relative humidity of the ambient air. Expelled large droplets were carried ... less than 1 m away at a velocity of 1 m/s (breathing)." -- https://onlinelibrary.wiley.com/doi/full/10.1111/j.1600-0668...
Hence the idea of social distancing (for airborne droplets) and frequent hand washing (for surface contamination). (And, of course, staying home if you have symptoms like coughing or sneezing.) Convincing people to use masks consistently and correctly has previously been shown (and remains!) to be an uphill fight.
(I note that there was a meeting of epidemiologists in March, 2020, where famously, no one wore masks. How far are you willing to to go to lie?)
Later, it was found that viruses could be carried by much smaller particles, much farther.
"Our laser light scattering method not only provides real-time visual evidence for speech droplet emission, but also assesses their airborne lifetime. This direct visualization demonstrates how normal speech generates airborne droplets that can remain suspended for tens of minutes or longer and are eminently capable of transmitting disease in confined spaces." -- https://www.pnas.org/content/117/22/11875
> "Well, the reason for that is that we were concerned the public health community, and many people were saying this, were concerned that it was at a time when personal protective equipment, including the N95 masks and the surgical masks, were in very short supply. And we wanted to make sure that the people namely, the health care workers, who were brave enough to put themselves in a harm way, to take care of people who you know were infected with the coronavirus and the danger of them getting infected."
I've heard this argument several times. I don't buy it at all. They could have instructed people to make their own masks especially since everyone was stuck at home. There is no shortage of fabric that I'm aware of. It also would have given manufacturers more time to produce masks.
Also, it's not okay to lie to the public, especially if you're supposed to be non-political. They deliberately lied and didn't apologize. There's no way I can trust someone who does that. That's not how my brain works.
It's clear that some medical professionals felt the science wasn't there, and ofcourse it wasn't. The science takes a long time. i.e. there was no science that showed that for Covid19 the use of masks would make a difference. Sure, it's common sense, but medical professionals don't use common sense. There might have been some papers about the Flu (with mixed results) and there were some other random papers, but there was no clear evidence either way. If touching the virus and then touching your face is the primary vector then it is possible that masks make things worse. Again, to me it was always common sense you should wear a mask (and not touch it and not touch your face) but even here on HN people were arguing both ways given the existing papers/publications.
Then there's the nature of public health, where your messaging isn't necessarily about what's the right choice for an individual, but rather what's the right choice for the public as a whole.
I don't think the public would understand the nuance of make a mask vs. buy a mask, ofcourse there'd be a run on PPE. Even with the message there was a run on PPE. Good luck trying to find an N95 mask in Home Depot last year in the first few months of the pandemic.
I'm not sure what's the takeaway here, public health officials, and medical professionals are not really scientists, they don't communicate science, they have their own objectives. Generally their objectives should be aligned with our objectives as a public but they may not be aligned with our objectives as individuals within that public.
The bigger issue to me is how slow the response has been across the board in most places, because all those bureaucracies move at the pace of a snail, pretty much every country on this planet botched the initial handling of this (of special note is China ofcourse) and blew away our chance of containing this early on. By the time we were on the mask vs. no mask debate the die was already cast (and a lot of people wore masks anyways and a lot of those who didn't wouldn't wear one anyways).