Inefficiency wouldn't matter for hunter-gatherers, as they're not the ones that feed the animal (they hunt, don't farm). Also pretty sure that dog-eating isn't a recent things, I don't see why people "back then" wouldn't eat stray dogs in periods of low resource.
More importantly, inefficiency most definitely isn't the reason for which people on the internet "become very angry" at the idea of eating dog.
It most certainly would matter for hunter gatherers. They hunt and they would be hunting the same prey as the dogs. They are feeding the dogs by giving up some of their potential prey as food whether thats by giving it to the dogs after they kill it or allowing the dogs to kill it and eat it instead of them.
More importantly, inefficiency most definitely isn't the reason for which people on the internet "become very angry" at the idea of eating dog.