Alcohol doesn't help social anxiety except by social convention.
Society believes alcohol changes personality, and that drunk people are less themselves. Thus, they judge drunk people less harshly (including themselves).
But alcohol doesn't actually change personality. It only makes your brain work slower. It doesn't make it go anywhere it otherwise wouldn't, you just get there later.
What we've developed is a way to split up when we're accountable. I promise you that split is zero-sum: the more leniently they judge your social behaviour when drunk, the more harshly they judge it when you're sober.
Alcohol absolutely does help social anxiety by improving mood and lowering inhibitions on a brain chemistry level. There are plenty of factual and scientific reasons to dislike and discourage alcohol, the "it's all in your head dummy" angle isn't one of them.
If it was simply on a brain chemistry level, why does it work so differently in other times and places?
It's an example of bad high-status science suppressing good low-status science. Neurochemists asking, "Why does alcohol make us do this?" without checking with cultural anthropologists if it actually does make us do this, or if it just makes "WEIRD" people do it.
I did not say it was all in your head, by the way. The lower reaction times and slower thinking is obviously real (and present everywhere).
I understand your point and would have to read more deeply about it, but these things exist on a spectrum. Anxiety reduction, talkativeness, etc. might very well be socially induced with alcohol making you significantly more susceptible to the social cues. That isn't any more placebo than any mood altering substance.
Society believes alcohol changes personality, and that drunk people are less themselves. Thus, they judge drunk people less harshly (including themselves).
But alcohol doesn't actually change personality. It only makes your brain work slower. It doesn't make it go anywhere it otherwise wouldn't, you just get there later.
What we've developed is a way to split up when we're accountable. I promise you that split is zero-sum: the more leniently they judge your social behaviour when drunk, the more harshly they judge it when you're sober.