As far as I know... there are zero reputable scientists stating there is conclusive evidence that mask use in the general public will significantly reduce transmission.
This coronavirus is new, so it can be assumed that any studies regarding the efficacy of wearing masks are based on no more than a few months of observation. It's doubtful if large-scale controlled studies resulting in conclusive evidence have even been done. Researchers continue to discover new things about this virus and we've already seen medicines hailed as miracle drugs one week and their use suddenly discontinued a few weeks later. So I doubt the final word on covid-19 and wearing masks in public has been proclaimed.
Masks also serve a social function. Most cloth masks don't seal effectively enough to prevent infection by the virus if it's present in sufficient quantity in the air that surrounds a healthy person. But that risk itself can be mitigated by other
people wearing masks, that is, those people with
the virus (who may not even know they're carrying the disease). By preventing corona-carrying droplets of breath from being propelled at someone's face and have the cough — or sneeze — or drunken boast — captured or deflected by a mask isn't a bad
thing. The existence of asymptomatic covid carriers makes the use of a mask more appealing for people who may have been exposed. Wearing masks even if they only promote a general sense of a shared social undertaking may still serve a useful purpose in a national emergency.
The real way to stop the spread of the virus is social distancing.
In a way, masks are
a form of social distancing, just on a more intimate scale.
The best hats are made of copper. In the shape of a pyramid.