Viruses do not travel alone in the air, they travel in flugge droplets of different sizes. Even in aerosols. Among all those infected, there is an approximate percentage of 10% of super contagion, they are asymptomatic, and in a mass event they can infect dozens and dozens of people, unless they wear a mask, if we all wear a mask, those people will also wear it , reduces the viral load that can leave them when you breathe, and enter the airways of other people, this reduces the probability of developing serious symptoms. Find out from serious sources.
It's never too late to stop being an anti-mask idiot