Wow, I couldn't agree less.
Addiction was by no means a voluntary and purposeful behavior for me - I'll certainly concede it was the result of my behavior, though. And I'll even agree that drinking on some level was always a choice even the times when it really and truly felt like I had no other options.
I've never ever encountered an addict who got there because that was their purpose.
And I've met and interacted with a LOT of people who are or used to be addicted.
O