The problem is, we're not in the game for "one drink". We don't get that special feeling we crave from just one drink. We're in this to get buzzed and drunk, and once that euphoria hits us, we only want more of it.
There is no such thing for me as "one drink". I will drink as many as I can until I pass out. That's how I learned to drink and anything less than that is completely unsatisfying. Therefore, I choose to have nothing at all.