Alchoholism is as much a disease as homosexuality is.
It is a learned behavior. The reason it "runs in families" is because over generations the behavior is ingrained in every person in that family. They learn to respond/react to these behaviors and pass them on to their children, and their children's children, much like an old family recipe.
The only reason that it is now defined as a "disease" is so the insurance companies will pay for theray...and isn't it convenient that alcoholics are forever "recovering" and never "recovered?"