It would be nice to have actual trials that show that masks are effective at reducing transmission (transmission, not stuff like reduced droplet emission etc).

This BMJ blog post[1] argues (and I agree) that if we're able to make trials for drugs, why not for non-drug interventions? Note that it is not against such interventions, but suggests we do trials to better direct public policy.

[1] https://blogs.bmj.com/bmj/2020/08/28/margaret-mccartney-we-n...