"Only" is hyperbole here. In my experience, I'm very tightly wound most of the time, and the disinhibition effect of two or three drinks works wonders for my assertiveness and confidence, and actually focus some of the time too - since I'm not fixating on worrying about a task or situation, I can put all my energy into actually doing it. Do I NEED alcohol for that? No, obviously. But it speeds up and simplifies the process considerably, so the benefits outweigh the drawbacks.
As has been said, the issue is that one or two drinks can very easily lead to eleven or twelve, and depending on the person problems can start at any time between then (or later than that of course). Knowing where to stop is key, but the disinhibiting effect of the drink also deprives you of your willpower/capacity to actually do so, so must be taken into account ahead of time. Ie, if you think, sober, you can stop yourself after 6 drinks, it's a good bet that after you've had those 6 you'll be too loose to do so, so you should really stop after 4.
My name is Addy. Please call me that instead of my username.