1.He shot once.
2. Just b/c the Coyote was not threatening anything at the moment does not mean it would not in the future.
3. Coyotes are grossly over populated in many areas of the US. Populations beyond anything seen pre-European just like deer. The food chain/circle of life is all screwed up and there is very little competition for what are now top predators. Humans need to fill in for wolves and bears every once in a while.
4.You sir, have never raised livestock or you would not be ignorant of these things.