You can always go for a demonstration. Tell them to wear a mask and spit in their face on the mask. Then ask them, would you like me to do that again without the mask? Did it work?
That would not work because they will show you a study that the virus is airborne and its much smaller than the fabric of your common cloth mask. They would say because of that the Virus doesn't stay within droplets but is passed from your breath.
And they would be right while completely missing the point. Masks, like social distancing, reduce spread. They don't prevent it, you're still not 100% safe with a mask, estimates only go up to 90% effectiveness for masks and that's for good quality masks. However when Rt is 1.8, stopping 50% is enough to get Rt below 1 and the virus will die out. Of course a little basic understanding of math and probabilities in particular helps.