It seems to me that for my entire lifetime I have been advised that if I sneeze I should cover my mouth and nose (sneeze into a handkerchief or my cloth-covered upper arm if I can do it in time) -- not to protect myself from my own germs, but to protect other people from them.
This has always seemed to me to make perfect sense.
Today, I have not taken a covid test. Today, I have no idea whether I have covid or not. If I have, and if I sneeze, I will be spreading my covid germs for several yards/metres in front of my face if I don't cover my mouth and nose when I do it. Sneezing sprays out from you, if it is not blocked.
Covid doesn't have to be sneezed. If you have it, you are breathing out the germs the entire time. How far does your breath go? I don't know: depends whether you are huffing and puffing and so on, but it won't stay in a nice neat bubble just outside your face.
Why wouldn't I be prepared to protect as much as I can someone on chemo, or someone immunosuppressed, or someone with a heart condition, or anyone who for whatever reason cannot at the moment be inoculated against covid, from my germs perhaps causing their death or long-term illness?
Yes, a mask will not confine my germs entirely to me. But it will very much reduce the amount of them that I am spreading around, and the distance I am spreading them to.
I hate masks. I hate wearing them, because they make me breathless at times and I have to pause where I am and breathe for a bit to recover. I hate people not being able to see that I am smiling at them, I hate not being able to see other people smile, I hate the whole business -- but I'd also hate to give someone covid and perhaps cause death or lasting health problems for them. And since people I talk to are mostly people I quite like, it seems a fairly crappy thing to do to people I quite like! In the same way, I don't have anything actively against people working in the shops, and if they can't do it because they are ill I wouldn't be able to buy things from them, so I'm spitting in my own cornflakes if I put them at risk.
(I don't wear a disposable mask. I wear a two-layer cloth mask with a paper filter inside it. When I get home I throw the paper away into the paper bin outside the house, wash the mask in hot soapy water and wash my hands thoroughly at the same time, then hang the mask to dry. The idea of throwing away disposable masks all the time makes me cringe for the environment, and I hate having to throw away a lot of bits of plastic every time I take a test.)