Or perhaps it's some unknown combination of all the factors that you can think of, but no one really knows because the very illegality makes it difficult to determine.
This means logically, you have to ignore the preconceptions, because they have no basis in reality, just your biases.
It ultimately comes down to the concept of personal responsibility. Drinking does not absolve one of their subsequent actions and choices, regardless of their subsequent "mental state". Any choice to have an "unsound mind" was made while of sound mind, and thus responsibility for all results lie with the person themselves. Being mentally impaired doesn't magically transform someone into a blameless zombie.
Colleges seem to be doing their best to erode this concept, but I digress.
There's an article I linked to in another comment subthread, it deals in details with this issue - in particular, when we should talk about personal responsibility and when just call it an illness.
I don't see why the two are mutually exclusive. In the article you linked, the husband is right for making it clear that it is Sandy's problem, the doctor is also right for recommending medical treatment, and Sandy is right for seeking the doctor for help solving her problem.
What isn't right is things such as the doctor telling Sandy that obesity is "primary genetic". Even if the statement is scientifically correct in a narrow context, it functions to absolve Sandy of responsibility for solving her own problem - whether it be by dieting, seeing additional doctors, exercising, or all of the above. Heck, telling her husband "I am fine with my weight" is in this same category of self-actualization, although she must accept others' inevitable reactions.
As for my comment, I certainly wasn't meaning to advocate "personal responsibility" in the sense of "let them suffer". In aggregate, addiction should be addressed as a public health problem. But that doesn't mean we should absolve the individuals of responsibility for their own actions because their brain has been chemically altered. This is what I was getting at, because that junk reasoning is used to justify inebriated behavior as nobody's fault, which is then used to justify a sweeping bans on altering one's mental state.