because someone doesn't want to wear a mask is not a valid argument against mask-wearing.

I realize that the virus will spread, and my sister and BIL may not have contracted it through non-mask wearing, but that also doesn't minimize some of the positive effect that wearing a mask and social distancing can have on the spread.

One last thing I noticed: I have been teaching classes through Zoom and so my computer is right in front of me. After a couple of days of teaching I noticed how spotted my screen was just from moisture that comes out in conversation. That wouldn't have been as apparent if I wore a mask, which is not logical for teaching online classes.