Alcohol is a social lubricant.
In moderation it brings folks together and contributes to cohesiveness between folks with differing viewpoints.
It greases the political wheels as compromise is far easier when you've partied with those on the other side of the aisle.
As an example, after Clinton was elected Washington turned into a wide open party scene every night. Regardless of your beliefs or your opinion of the outcome, you can't deny that the ability of the House & Senate to compromise during the Clinton administration was far better than at any time before or afterwards and that this compromise contributed to one of the greatest eras of peace and prosperity in the history of mankind.
I'm not saying alcohol is the reason great things happen, but it is a piece of the puzzle.