I would like to second the "think of the children" argument. My father drank a similar amount and also said "(which is not that much, certainly I got used to it, so it doesn't put me in the drunk mode neither)". But he was irritable when he drank, and I remember playing a game where I'd come up and talk to him, and then run away laughing as he chased after me and knocked into the furniture.

It is easy to think you're sober when you're drunk.