So 70k people signed something (that, as pointed out, has nothing to do with masks).
How many DIDN'T sign it.
Somewhat like the "1000 engineers and architects" that signed the thing about the way the WTC towers collapsed being 'wrong', knowing how large the population is counts.
And yes, I may not know about the subject, but I know how to apply critical thinking.
I can usually do a decent job of sorting out 'real experts' from the frauds.
Sources also help.
I'm far more likely to believe an 'expert' on NPR/PBS or BBC vs one on Fox.
Viruses travel within droplets, which are blasted out of the mouth. Masks reduce droplet expulsion.
One of the earliest times I was seriously scared of Covid was when it was discovered there was pre-symptomatic transmission. That people could be contagious before they showed symptoms.
There was a story that came out of the Pacific Northwest (Washington? Oregon?) where a church choir had a practice. 2 people were infected and contagious, but not yet symptomatic. 3/4 of the people present contracted Covid. A few died.
Along a couple reports of that story was a silhouette picture of a singer. Strongly backlit, you could see the quantity of droplets being expelled.
Masks help control that spread.
Not 100%, not perfectly.
Masking, along with distancing and handwashing, the spread was reduced.
One of the best indicators of the effectiveness was the spread of influenza.
With the mitigation practices in widespread practice, spread of the flu was sharply reduced. One strain of the flu is now believed to be extinct.
Of course, the idiots refused to comply.
I've heard the term "Defiant Oppositional Disorder", which is a fancy word for 'acting like a toddler who only says "NO!!!!"'.
This was seen a few times when the idiots were refusing to believe that Covid was serious, that masks were effective and (of course) believing that Covid was a Chinese bio-weapon and that the vaccines were either deadly or contained 'tracking chips. My favorite was a schematic of these 'tracking chips' that went around.
It was an effect pedal for an electric guitar.
https://www.guitarworld.com/news/the-creator-of-the-covid-vaccineboss-metal-zone-pedal-hoax-reveals-all-there-aint-a-lot-of-sane-people-in-this-world
Turns out it was a hoax, from a guy who wanted to make the conspiracy idiots look like...
Idiots.