The fact that there’s any controversy about this at all leads me to believe that many have abandoned all reason.
This is a moral judgement and not everybody shares the same values as you, especially regarding what a "reasonable" chance is. Some people don't believe they should inconvenience themselves just because it would contribute to a tiny decrease in deaths. There's also an absence of data: given we've got months of data on death rates and mask usage rates in different areas, it should be possible to quantify exactly how strong the correlation is, but nobody's even done this.
It’s not a moral judgment, it’s a foundational element of all functional human societies. If you don’t agree, you should remove yourself from society.