A New Scientist book review:

In the face of life’s inconvenient facts – alcoholism, drug addiction, depression and craziness, to name a few – pseudoscientific medical concepts allow us to cast difficult moral problems as simple factual questions, readily soluble in the lab and in the hospital. Gary Greenberg’s The Noble Lie is an impressive and fascinating round-up of such pseudoscientific notions and the ways in which they have come to count as genuine illnesses.

For instance, Greenberg explains how alcoholism’s transition from vice to disease was a welcome one, especially following Prohibition. It was long viewed as an allergy, though the specific allergen persistently failed to appear. Even today, neither its disease-nature nor any possible cures have manifested themselves. Regardless, people are happy to accept the idea that addiction is a medical illness, perhaps, Greenberg suggests, because of our ambivalence towards the role of pleasure and our uncertainties about free will and self-determination. "With the disease model we have an answer," he writes, "one that has the imprimatur of science; addiction isn’t wrong, it’s sick."

In the absence of scientific proof that addiction is a disease, is it wrong for medical professionals to perpetuate the idea? Not necessarily, Greenberg says – there are times when what is scientifically wrong, or at least uncertain, is morally right. "There can be no doubt that the disease model has helped millions of people. If a made-up disease can be of such immense value, then we must consider the possibility that the truth is not what it’s cracked up to be. Perhaps, in the republic of medicine, the fiction that addiction is a disease is a noble lie."

Sometimes the noble lie works the other way round. In a chapter on homosexuality, Greenberg shows how humane concerns first led people to prefer a medical to a criminal definition, but conflict followed concerning the disrespect a medical definition implied toward what should perhaps be viewed as a free life choice.  In 1973, following the Stonewall riots and the start of the gay rights movement, the American Psychiatric Association deleted homosexuality from the Diagnostic and Statistical Manual of Mental Disorders (DSM), a move decided not by scientific facts but by political and moral attitudes. "It may be the first time in history that a disease was eliminated by the stroke of a pen," Greenberg writes. …

In a fascinating correspondence with the clear-headed and callous murderer known as the Unabomber, Greenberg tells Ted Kaczynski that he should never have been forced to accept the defence of schizophrenia at his trial, both because he believes Kaczynski was in fact "evil and not sick", and because "his very character seemed to bear the imprint of large social and historical forces" which could not be investigated once he was classed as too mad to be taken seriously.

People quite reasonably have different categories in their minds for disabling conditions; they distinguish diseasese, deliberate choices, weaknesses etc.  While there may be ambiguities at the boundaries, these seem reasonable categories to use.  You might not approve of how people choose to treat people in these different categories, I have little much pateince with lying to folks about what behavior falls in what category just to trick folks into treating folks the way you would prefer.