Common sense seems to say that masks make s difference, but if that is the strongest argument, then why not let people decide for themselves using common sense.
The wearing of masks to combat airborne disease spread is a decidedly not a new thing. That was never a novel concept, at least since the early part of the 20th century.
Coronaviruses in general aren't a novel concept either; we have a pretty good idea how they're spread.
So, when confronted with a new coronavirus, it's a little bit stronger than "common sense" to surmise that masks will be effective to some extent. The burden of proof would be on anybody suggesting that this virus is somehow so different than other airborne disease that the wearing of masks had no benefit.
then why not let people decide for themselves using common sense.
If masks are effective to some degree, the downside to not wearing masks was that millions of additional people would suffer and die worldwide, and we would incur a financial and human cost orders of magnitude greater than the modest cost of masks.