That is not at all what I mean when I call it a disease, it doesn't excuse their behavior in the slightest, nor does it justify their behaviors.
It explains why it is so difficult for them to make good choices. The problem an addict has is not so much with a particular substance it's with the addictive tendencies (disease). Nine times out of ten, you take one substance away they will become addicted to something else chemical or even non-chemical. You have to address the disease, not just the symptom.
Add in the fact that many addicts start using when they are very young, when their brains are still developing. They don't follow a "normal" developmental path in the slightest, oftentimes their brain/behavior is extremely stunted and they literally have to "be their own parent" when they sober up and finish growing up the rest of the way. Not to mention that they oftentimes made the "decision" to use when they were near babies in terms of understanding actual consequences and often suffer from other mental illnesses. It's no more simply a choice to sober up than it is a choice for a person suffer from severe depression to "just be happy."
There are a lot of factors that go into a addiction, none of which excuses or justifies what they do in the throes of their disease. However, understanding these factors enable us to understand why they are doing what they are doing in hopes of actually helping them sober up and stay sober. If it was as simple and as easy as a choice there wouldn't be very many addicts out there at all, you'd only have to haul them in, let them dry out for a week or so and 95% of them would make the choice to be sober for the rest of their life. The life of an addict is miserable.
Anyways, I could go on about this all day, I have a lot of experience with addicts and their issues.