Opiates are relatively non-addictive if their use is regulated intelligently, which for some reason all people can't reliably do themselves.

The question of what is or isn't addictive and why is important but it's a little beside the point. I am happy and perhaps eager to discuss addiction in the context of dieting and obesity, but at the outset we need to agree on a definition of "addiction."

My point in bringing up heroin is that it's basically impossible to separate the good aspects (analgesic) and bad aspects (addictiveness) of morphine because both qualities are the result of the same mechanism. Analogously, it's (in my opinion) impossible to separate the good aspects (tastiness) and bad aspects (fatteningness) of foods like doughnuts because both qualities are evidently a result of the same mechanism.

Actually I am tempted to go further than that and hypothesize that in both cases a big part of the problem is the part(s) of one's brain which process pleasurable experiences.