I do understand alcoholism but luckily only from a textbook perspective. I do know that at its absolute worst, the vitamin deficiencies do cause severe, permanent brain damage. Mel can't be that far gone yet and thus remains responsible for his behavior. AA would agree.
He was a drunk for years when he was younger. I saw a Kiefer Sutherland interview in which he talks about blackouts and having no idea what he did. There doesn't need to be brain damage for there to be blackouts.