I agree to that,but masks are still useful even for preventing, and my main reasoning was that wearing a mask is a proxy for how serious the person is for all t

I agree to that,but masks are still useful even for preventing, and my main reasoning was that wearing a mask is a proxy for how serious the person is for all the rest -- social distaning, avoiding crowds, avoiding interaction with people who don't wear mask themselves and so on. But as someone else commented -- retrospective studies probably are not that useful.