For anyone who likes to point out that their parent who smokes is a tzaddik in all other ways, and I totally believe you, substitute alchohol for the smoking addiction. No matter how wonderful that parent may have been all your life, would you defend alcoholism the same way?
But oomis, in all fairness- smoking is not mind-altering. Alcoholism is. An alcoholic parent is impaired in a way that a smoking parent is not.