This! The fact is that in "the wild", so many different factors are at play that it's very hard to establish the impact of one particular factor on the numbers

This! The fact is that in "the wild", so many different factors are at play that it's very hard to establish the impact of one particular factor on the numbers. In a sense, establishing the exact impact of wearing or not wearing masks is as difficult as establishing the exact impact of the population pyramid on how things evolve. Combine both and things become even more obtuse. Worst case is that one ends up confounding correlation with causation which leads to harmful conclusions. Such as over reliance. What you are saying is the rational sensible middle ground in this discussion. Most domain experts are very careful in the type of recommendations they make. I'm not a domain expert, and so I put my trust in domain experts. I haven't heard any micro biologist or health care expert urge wearing masks as a basic necessity. I do hear them urge to vigorously wash hands, practice physical distancing and generally stay at home as much as possible...