The definition of all mental disease is completely based on social norms, a mental disease is just something which prevents you from behaving in a way certain people deem 'normal'. People like Szasz have posited it as a method for social control, where psychiatrists are proxies for authoritarian state power. I think if you asked Nietzsche he would say it's a natural response to the death of god; people look for something else to worship, and it's capitalism/obedience, and people who don't believe in it need help much in the way heretics of old were deserving of our help and pity to find God. Now instead of priests we look to psychologists, the priests of our new religion.

If you need evidence simply look at homosexuality; this was a mental disease while society didn't accept gay people (being gay made it impossible to live a "normal" life in society). Now that we think being gay is just fine it's no longer a disease. Nothing medical changed, ergo the definition was not in essence a medical one.

"If drug addiction is perceived as a symptom of a sick society, suddenly the logic of treating it is completely different."

Couldn't agree more (see my post elsewhere in this thread). I think the campaign against addicts (drug war) was indeed started from the 'isn't useful to capitalist society' angle, but now addicts, at least in the US but I'm sure pretty much everywhere else, are actually what bring massive profits to capitalist society through our government's prosecution and persecution of them. While it probably was not the intended result for most prohibitioners when they started the drug war, the war itself has created a whole new multi-billion dollar industry and front for many capitalists, especially the manufacturers of weapons, law enforcement, etc.

Society, at least in the US, refuses to look at itself as the source of the problem because it enjoys the problem. Much of society has benefitted from persecuting and prosecuting drug addicts and the inevitable supply lines that are caused by the existence of a black market. Police, military, politicians, and other beneficiaries of all these billions (trillions over time) refuse to ever acknowledge there is a problem because that would mean the end of their nice perks, the end of the pina colada machines in the police station, the end of the fun SWAT raids, the end of selling so many assault rifles, tanks, and other death equipment that doesn't belong in civilian police hands.

Damn straight addiction would be treated differently if it was seen as what it really is: a symptom of an incredibly sick society that no longer cares about its members and values profits above all else, including all human life, even that of its own citizens.

>How many diseases are "isn't productive under capitalism and is therefore less useful to society" syndrome?"

We tend to call those "crimes".

Just like drug possession and use? :3

Every institution of power has its own designator of "bad" that justifies dehumanization. Police: Crime. Medicine: Disease. Military: Terrorism (nowadays). Religion: Heresy. etc. We should not be surprised when they overlap.