Dear Karens*,
At the cornerstone of civilisation, basically dating back to the very beginning of when humans began to gather into communities, and do something other than hit each other over the head with a rock, is something called empathy.
empathy
noun
the ability to understand and share the feelings of another
By showing empathy, humans have been able to accomplish great achievements - like say making the iPhone - because we have learned how to get along with one another (without those aforementioned rocks), and put ourselves into other people's shoes, to think of someone other than ourselves.
Whilst you may be perfectly healthy, and not in the age bracket which COVID-19 is massacring globally as we speak, by walking around without a mask on, you could potentially spread the virus to others who are in the affected age groups. You as such would be hastening someone's death - possibly a great many someones.
COVID-19 may only cause mild flu like symptoms - for young healthy people - but there are also plenty of healthy young people who are now dead due to COVID-19. Over 20,000 people under the age of 50 have died from COVID-19 in the USA. Meh - guns kill more in that age bracket, I know.
Whilst the official death toll for COVID-19 is "only" half a million (USA only of course) - if you count people who fell ill with COVID-19, and then died from complications such as pneumonia or asthma - the real death toll is close to 4 million people.
How many people need to die for you to give a damn about this?
* Please Google "Bunnings Karen" to see if this message is intended for you, although I suspect you will know just by reading it.