I don't really like the word disease so much either. But I definitely think it is a mental illness.
I think of cutters, hoarders. What they do is obviously so destructive and, "SICK."
Yes, we do indeed do it to ourselves.
I feel like mental illness makes much more sense. There have been so many times that I am putting the bottle to my lips as I curse myself, hate myself and know not single thing positive (other than very brief relief) will come from it.
No, it is not cancer. But if that is not sick, I don't know what is.