Re-read what I said. I said *every single time*. Coyotes need to learn to fear humans. Every interaction with a human being should be a negative one for a coyote.
Now, thinks about it... what percentage of Canadians can legally fire guns? Do you have a gun with you *every time* you are out in the woods? Is every spot where you might meet a coyote one where you can legally, or safely, discharge a firearm? Hell no!
Hence rocks.
Coyotes explore unfamiliar animals by having a series of progressive encounters where they become more and more bold and daring. When they come to the conclusion that humans are large but slow, bumbling animals that coo and aaawe when they spot coyotes and don't seem to have any offensive capability whatsoever, they will start wondering how we good we tastes. Coyotes should learn that humans are unpredictable, short tempered animals, not two-legged food...
Of course, if you are in a position to shoot the coyote, then shoot. But in most cases, for most people, rocks, sticks and yelling will be more achievable.