A diagnosis of 'mental illness' - ie a consistent aberrant behavioral pattern within definable parameters - is too often an example of condemnation by statistics rather than a diagnosis of specific brain dysfunction. Indeed there are those (other than the Scientologists!)who would argue that the term 'mental illness is itself meaningless - behavior is simply behavior with no classificatory dimension at all.
Even the the full-on psychopath is not 'ill' by his/her own standards or the standards of other diagnosed psychopaths.
As Bertrand Russel is said to have remarked "the only reason that one who believes himself to be a fried egg is said to be in error, is that few people agrees with him".

I quite liked the article and strongly agree that we seem to be stretching the parameters of mental illness. Particularly when it comes to behavioral disorders in children and depression in adults. Depression is perfectly normal in most cases and is the bodies way of slowing us down and getting us to think about our lives and then make the necessary changes in order to be happy again. However, when we say it is the result of a chemical imbalance, and treat it with tablets, we fail to make those necessary changes. Of course there are some severe cases of pathological depression which do require pharmacological treatment, but they are relatively rare.
The constant talking up of the numbers of people with mental illness (1 in 4?) is a real a problem. It seems anyone who is unhappy, likes to get drunk or use drugs, doesn't like the way they look or has sex with too many or too few people is placed in this category.
However, I do think that diagnosis is important for treating genuine mental illness. If you don't know or haven't defined what you are treating, you run the risk of continuing to add in more pills when the patient fails to improve. This is particularly the case with borderline personality disorder. Clinicians are reluctant to "label" someone with this diagnosis as they perceive it be stigmatizing. They prefer to say its "major depression" or "psychotic depression" or "adjustment disorder" or "PTSD". However, when the person fails to improve they add in more and more medications. I frequently see these people on 4 or 5 different psychotropic medications, experiencing exactly the same problems they had to start with, as well as the obesity and poor health that comes with the medications.