This sucks

Using different countries as cohorts introduces all sorts of confounding factors.

People will put forward a biased case even without a financial incentive. Maybe a person genuinely believes that the weight-loss or skincare regimen they followed worked, and they want to put the best case forward so other people benefit from it, so they use the worst Before and best After photo to be more convincing. People who saw no difference won’t post at all.

The reason RCTs exist is because time and time again we’ve seen that looking at anecdotes and individual case studies leads to conclusions that turn out to be wrong when you RCT them. Might seem nitpicky but you just end up wrong half the time otherwise.

In 2016 I took part in a novel drug trial in Brisbane, Australia that injected me (and about 6 other men) with the Plasmodium falciparum strain of malaria and then treated us with a new medication called SJ733. The development of SJ733 was funded, I was told, through Bill Gates' Medicines for Malaria Venture. The paper about this trial (and some other trials) came out in 2020: https://pubmed.ncbi.nlm.nih.gov/32275867/
Results were positive!
Seems like work on it continues: https://pubmed.ncbi.nlm.nih.gov/35598441/ 
I gave the $2880 they gave me to the Against Malaria Foundation. It's one of the best things I've ever done.

I didn’t see case-control studies or cohort studies. You should link to those.

Before and after photos are prone to manipulation and bias
Take a photo with your jaw pulled back for the before and then one with your jaw projected forward for the after. Use better lighting for after. Even if the person is not consciously intending to, these are so easy to manipulate.

Maybe surgery was done in some of those photos and the poster is not being forthcoming about that, if they have something to sell.

The evidence for mewing just doesn’t seem to be there. You give a lot of theory and anecdote and before/after photos, which aren’t worth much. The main proper source I see you list is https://academic.oup.com/bioscience/article/70/9/759/5872832?login=false, which itself seems to admit that there’s a lack of evidence for it

Another cost with a failed moonshot is damage to reputation. If I think that there is a 5% chance of another pandemic in the next 10 years and I spend the next 5 years working to mitigate it, there is a 95% chance that everyone who tells me I am crazy will end up looking like they were right.

Interesting I wasn't aware that The Life You Can Save and Founder's Pledge had this fund going. Thanks. I don't have an an answer to your question.

Alternative response: If someone told me that there was somewhere between a 0.00001 and 0.5 chance that I was to be struck by lightning tomorrow, it would not be reasonable for me to say “well almost everywhere within that confidence interval I have a >1% chance of being hit by lightning tomorrow”

Almost everywhere within

Most of these CIs start at zero and they can't go below zero so shouldn't we consider these on a log scale? In which case the scale goes back to negative infinity and "almost everywhere within" is meaningless.