And you apparently haven't had the same with a dog, especially if you can talk about eating them. I don't eat my chickens nor my dogs, both get to be all they can be.
I have many experiences with many dogs, both good and bad. I have a pretty close relationship with my dogs, and I allow them to do what they were bred to do. I don't make them wear sweaters, or humanize them, nor do I believe in prolonging their lives to protect me from the pain of their passing, at the expense of their suffering.
What animal is food, and what animal is taboo, is largely a product of the culture you were brought up in. The only backwards way of thinking is to think that one animal is edible while another is not. If you don't eat your dogs, or your chickens, that is your prerogative. Just know that there are cultures that don't share your view.
Know also, that there are cultures that have had chickens for a very long time, certain birds are considered very sacred, and are even given funerals. It is hard for us to imagine, but if you experience the type of birds that these people interact with, and the level of interaction, it is easy to see how a chicken might be considered more of a one on one pet and less of a barnyard scavenger left to it's own devices, except when stealing eggs, and harvesting excess cockerels.
There are chickens that crave human attention, that strongly dislike being around other chickens, will interact with it's people, begging for food, tolerating handling, adhering to boundaries, and be quite stunning to look at. If you haven't had any, that is because you have had birds that weren't selected for those traits. Most likely you have only had birds that were selected for eggs and meat, and more recently pretty feathers. Until you have experienced all that a chicken can be, you really aren't an authority on what they can't be. Can they herd sheep or tree bear? No, but they can serve the purpose that most dogs serve for their owners, that of companionship, regardless of their inherited abilities at a specific task that caused them not to be eaten by our ancestors.
Keeping a chicken as a pet is no different than keeping a lab without being a duck hunter, or keeping a border collie with no sheep. Might not be the intent they were bred for, but they serve a purpose to those who feed them.