Actually my letter carriers love my dogs. Of course, they are in cars and my dogs can’t reach them unless I pick them up.
As far as I’ve ever read it’s assumed the symbiotic relationship between humans and dogs started out with proto-dogs following camp, displaying submissive behavior to humans, eating our trash and poop, and sounding the alarm if predators or enemies were near. That’s the function they serve in many undeveloped areas to this day.
Depending on the culture, as resources allowed they were then selectively bred as guards, for hunting, for herding, for carrying packs and pulling, as food, etc.