You know, so hard to really know, but I believe in the disease theory as well, just not the "said addiction" as the disease. I mean, to destroy oneself with any substance does disease the body, but there is a core issue to why someone wants to hurt themselves.
In our clinic, we do have recovering addicts as patients, and they come in to want to try to heal their bodies from the damage they've done. And each and every one has a diagnosed mental health issue, Most of them; depression.
I have panic disorder and never became addicted to anything. But I'm a recovering control freak and critical person <--- this is how I dealt with pain.
This is why I think addictions are just self medication. We all do it in some form.
We may never know, just my theories really