I think what you're describing is a procrastinator's fallacy- it's like saying I've waited this long so what's the point in doing anything at all now? I disagree with that approach to covid and public health.
You're right, it wouldn't make any measurable difference overnight but it will pay off down the road, and covid-19 is here to stay.
It would make a moral difference overnight. Right now the official party line is to mask shame the unmasked, including people who have made healthy choices all along- who are people who have taken personal responsibility and put in hard work to stick with those choices. Punishing the hard workers and rewarding the slothly, that's un-American