Amber Hollingsworth advises against telling someone with an addiction that they are a "terrible person" or using similarly harsh phrases (e.g., "you're such a screw up", "you're the reason this family's falling apart"). She explains such statements provoke defensiveness and suggests reminding the person of their better qualities as a more effective approach.
Chapters
The thing that you never want to say to someone who has an addiction is any version of you are a terrible person. Things like you're such a screw up. You're the reason this family's falling apart. You're costing us everything. You don't care about anyone but yourself. How could you do this to us? Now, I'm not even trying to argue with you and tell you that those things aren't the truth, or at least partially the truth. Because when you say something like that to someone, naturally they're going to get very, very defensive. Even if they're doing really bad things, deep down in their heart, they're probably not doing it because they want to be a horrible person. I'm not making excuses. I'm not saying it's okay. Mostly what I'm saying is just don't say that to them in that direct of a fashion. If what you really want is for the person to be a better person, then remind them of their better qualities. So much more effective.