OK. I'll say this once and then I will not reply to further nonsense...
Dogs have been "developed" from the wild canines of old (waaaaaaay old) to be shepards, protectors, and companions to Humans. At this point, leaving a dog to his or her own devices, i.e. "letting them leave", would be tantamount to abandonment of a child.
What, exactly do you think would happen to a dog if we were to "let them leave"? I can tell you what animal rescue workers will tell you; they will starve, they will become infested with parasites, if female and not spayed, will soon become pregnant and, by and large, unable to obtain enough nourishment to sustain themselves, much less their pups. If in an urban or suburban area, he/she will run a high risk of being hit by a car and killed...or worse...seriously injured. They will often fall prey to larger and tougher predators. They will have no safe harbor, no roof under which to rest when it rains, snows, or hails; no protector; no supplier of food; no one to love and provide for them.
We are not talking about wolves, wild dingos, foxes, or other truly wild animals, we are talking about domestic dogs; born and bred for generations to be companions, not frontiersmen.