This is an old debate that will never be resolved unless we can agree first on the definition of "disease".
Staying pickled in alcohol long-term results in a medical condition that provably exists and can only be cured by not drinking alcohol, which is increasingly hard the more and longer you've been drinking (and it's hard because of the medical condition you've drank yourself into). But is that addiction? So this gets dicey too, and we need to agree on the definition of "addiction" as well as "disease" before we can address the question, "Is addiction a disease?" This is why these debates never go anywhere, because the terms aren't defined so everyone understands what they are debating.
Certainly there is a genetic component, and for example twin studies show this. I think the consensus is, part of the susceptibility for becoming addicted (however you like to define it) to alcohol is genetic, the rest is environmental, probably roughly in equal portions.