Why on earth would you want to drink in moderation? <she sputters> You don't even get drunk that way!
Several people have already said this, but it bears saying again. For most alcoholics, the point was to get hammered, to lose control, to achieve a certain feeling. I've had a couple of people ask me if I thought I could control my drinking now -- after having been clean for a few years. My honest thought was, "What for? If I'm going to bother to drink, I'm going to get snot-slinging drunk."
People who are able to moderate their drinking (non-alcoholics) don't even have to think about doing it. They just do it. For whatever reason, they are not addicted to the sensation of getting drunk. These folks could honestly never have another drink and be satisfied with it.
I have never met an alcoholic would could take or leave alcohol. The drinking is either on or off -- like a light switch or a television set. Most alcoholics do great when they're sober. Once they pick up again, though, the insanity creeps back in until it has taken over their lives.