The first half of Kent Dunnington's book Addiction and Virtue is an attempt to tackle this snarly question. This not the part of the book that I want to focus on, but it's an important issue that lays the foundation for any theology of addiction.
We tend to moralize addiction when we frame it as a choice. Addiction, if it's a choice, is a sin and the addict is viewed as a bad person.
A key advantage, then, of viewing addiction as a disease--as a brain pathology--is that it marshals sympathy for the addict. Viewing addiction as an illness lowers moral accountability. We shift to treating addicts rather than blaming them.
There are two good reasons for viewing addiction as a disease. First, there appear to be biological correlates for addiction, genetics that appear to make some brains more susceptible to addiction. Second, addicts report a degree of compulsion that give the impression that, in the grip of addiction, their ability to exercise rational control has been compromised.
The general consensus among medical and mental health professionals is that addiction is a disease. And yet, this consensus is controversial and contested. Many professionals working with addiction think the disease model is wrong, and perhaps even harmful.
Regardless, if addiction is a disease it is a really weird disease. As Dunnington points out, most addicts recover from addiction and when they do it's often without any medical intervention. Some addicts just stop cold turkey.
Those cold turkey testimonies seem to reinforce the "choice" model of addiction. And yet, addiction is accompanied by such overwhelming and self-destructive compulsions that it's unlike anything resembling a rational choice.
In short, addiction is a paradox, falling somewhere in that murky interface between voluntary (choice) and involuntary (disease).
Our current theologies of addiction are ill-equipped to handle this murky space as we're pulled to either extreme, choice or disease. Dunnington's work is helpful as he uses Aristotle and Aquinas, the virtue traditions in Greek and Christian thought, to explore the interface of voluntary and involuntary action, the territory where addiction seems to live.
Borrowing from these virtue traditions, Dunnington suggests that addiction is best viewed not as a choice or a disease but as a habit. As Dunnington shows, the category of habit best fits the paradox of addiction, how addiction responds to non-medical interventions but is also experienced as an involuntary compulsion.
Having argued that addiction is best viewed as a habit (rather than a choice or disease), Dunnington then goes on to the second part of his argument, the part of his book I want to focus on.
Specifically, if addiction is a habit, what makes this particular habit so addicting?