I too struggle with the idea of whether it is a "disease"... to me it is a mental disorder if anything. The problem is that that disorder as a tendency to make them make bad choices, even tho they know they are making a bad choice.
I asked my wife how could she knowingly ingest something again that everytime she has done it it has resulted in nothing good coming about from it. Her answer was that her disease compels her to do it in order to survive.... for her disease to survive... funny thing is that her doing it will eventually kill her and the disease right along with it. However, there are parasites in the world that kill their hosts and thus take them with it.
Now, some of the other actions that go along with substance abuse to me are clearly choices... but just like anyone under stress/influence/etc... we do make bad choices. I am working hard to cut her some slack on all those bad choices... but while I may forgive her for making them, she does not get scott free of the consequences.
T