I too have struggled with the "Why can't he just stop drinking" question. I mean I'm starting to understand that alcoholism is a disease. This "thing" is new to me. I've never had to deal with someone who has this.
But my argument is this- Diabetes, for example, is a disease. Diabetics get cravings for sweets and sugars. They know that if they eat these "bad" things, they will become sick and possibly die from their disease. Alcoholics get cravings too apparently. Why can't they turn that switch off in their head/thinking that if they take that next drink, they will get sick or die?