Alcohol causes temporary loss of motor control and some brain functions, and this is exactly the point. Any mistakes can be blamed on ‘being drunk’, and thus people are able to cast of the shackles of social inhibition, and enjoy themselves more unimpeded. Our society is rather oppressive when it comes to making mistakes or looking ‘low status’ in normal situations, so alcohol is the perfect way for many people to compensate, and allow themselves temporary spans of time where they’re less afraid to make mistakes or look incompetent (and I would argue this general fear of making mistakes or looking incompetent is one of the main plagues in society, preventing all sorts of people from improving their lives).
Call it placebo if you want, but placebo is great if it works. Anything is great if it works.
I’ve never noticed it used as an excuse, and to me that seems a lot like saying “I was biased!”, to cast away blame. Though I have a different frame of reference—here you’re accountable for anything you do, sober or drunk, including making mistakes/looking incompetent. Where is the line drawn where you can just shrug off any blame? I can’t think of any rational reason to want to drink, then, unless you want to… Act incompetently and get away with it? Is this then a good thing?
I agree on the placebo bit, anyway.