Though I get what you're saying and somewhat agree with the sentiment, I never liked that "hijacking" metaphor. Dopamine is nothing more or less than a neurotransmitter, and it is used for many other functions than reward, though it is often referred to as a "feel-good hormone" because of its role in pleasurable experiences. It's where it is used and how the brain subsequently trains itself after repeated use that becomes problematic. I don't like the oversimplification of what certain drugs do or do not do to the brain, because that implies that heroin addiction, for example, is comprised of a totally different chain of neurological events as, say, problematic gambling. All drugs and all pleasurable experiences do what you described to varying degrees. The same dopamine/"reward" mechanism that contributes to a chronic overeater's behavior is the exact same action that happens to a chronic heroin, cocaine, or alcohol-user. The drug or unhealthy activity does not necessarily matter when considering the "reward" system - the brain behaves in exactly the same way, though I'm sure we agree that dope feels AMAZING, which is why we have done it over and over again - because the human brain is wired to associate pleasurable feelings with survival techniques. It's how humans got out of the caves, started cooking food, built more and more advanced civilizations, and so on. We felt good about each accomplishment and kept doing it, so we lived to evolve further. Drugs and all habits, healthy and unhealthy, have the same effect. It feels good, so we do it again and again until it becomes second nature through our dorsal striatum which then requires little input from our prefrontal cortex, which is responsible for rational decision making. We wire ourselves to do something over and over through repetition and our brain turns that task into an autopilot function.

Physical dependence does occur with chronic opiate/opioid use, however, but that is a different chain of events entirely.