Circular logic. What do you think "discipline" is? It's just a word people use to describe people with strong rational, goal-oriented behavior, with ability to follow through over long periods of time.

This is also called "executive functioning" and it's wholly dependent on your brain chemistry, i.e. the thing that is malfunctioning in addiction.

So yes, they lack "discipline" because discipline is also physiological, it's not just (and maybe not even primarily) a reflection of the person's character. By treating them as separate you're engaging in mind-body dualism.