An interesting article:
http://www.psychologytoday.com/blog/the-heart-addiction/201112/is-addiction-really-disease
I tend to view it as a mental issue (or illness) rather than a disease, per se.
I agree that some people are junkies who cannot be helped but they still matter to someone. I don't care about everyone in the world equally but there are those around me I can help. The trick is to know which ones genuinely want to help themselves, and help if you can without getting dragged down. Like a form of mental triage.
Regarding how creative people have used substances in the past to further their art, the list is endless, and not limited to musicians or actors. I know that certain substances unlock a part of my brain which my consciousness can sift through later. To get trapped by those unlockings is tempting.
IMHO, there are people for whom the present world system just doesn't work well. This is the age where you're not allowed to shut yourself off. You must remain plugged into some form of electronic system, whether it be a forum, Facebook, or even just be forced to have a bank account. The natural way of living is dying, and we are natural creatures, so this has a knock on effect in mental health and the issues that arise. The more we get plugged in (through necessity or desire) the more we find we cannot extricate ourselves. We have so much irrelevant news, so many media feeds that just don't matter pushing our psyche this way and that that our relatively primitive brain has difficulty coping with the sensory overload. Some substances act as a buffer, some as an enhancer which lets us become more effective, but both kinds allow us to cope by distorting our perception of reality. (I'm not getting into a reality discussion.....
) Those systems need not be electronic. Try living without a vehicle, or reliance on electricity, or whatever. It's different things for different people.
Personally I have ongoing mental health issues, and I'm not going into them. You tell someone, and they wonder why you can't cope, or worse, you get pity. I realise that what it really is is natures way of trying to weed out a part of the population using any means necessary as a form of population control, and if there's one thing to be said about nature, it's that it is ruthless. I know my triggers though, and that is the best possible weapon to have. People who suffer from addiction have their own triggers, but most addicts aren't aware of them before they become addicted to something.
There isn't anybody in any position to judge unless you've been in a similar situation, and if you have then the first human reaction is genuinely to help rather than to chastise.
Edit: Like Fabio, I'm bowing out also.