Defining categories would be a good starting point. An illness is not the same as a personality disorder is not the same as bad behaviour (or sugar induced hyperactivity!) in children or learning anomalies or grief or appropriate response to trauma. They can't be treated the same way. The only reason anyone would try treating them the same way is to make the 'problem' people keep quiet and stop bothering us.I regard it as a positive thing that this fact is nowadays being more widely recognised by the medical profession and I completely agree with Hobbes that this applies particularly to the question of treating behavioural disorders in children with mind-altering substances, the long-term effects of which are almost completely unknown.
At the same time, I strongly object to all mental disorders being classed as "part of the person" who suffers from them and therefore incurable. Nobody wants to be identified with their worst aspect. It's a bit like classifying people as lepers or cripples because they suffer from an infection or injury.
Some mental illness may remain forever incurable, but I think we ought to keep trying to track down and address the causative factors we are able to isolate*, and meanwhile, to alleviate as much of the suffering as possible, by all available methods.
(*Because some really are external to the patients and their life choices - I suspect there are far more contributory factors in the physical environment than we know about. As long as we tell we tell people to repair themselves or live with it, we'll never clean up.)