It's not just an increase in confidence or ability to socialize, and there's no inherent reason why friendships need to be shallow or dependent on alcohol like the phrase "drinking buddies" implies. Alcohol causes euphoria, plain and simple. I don't see any reason why responsible moderate use can't result in a net utility gain over the potential health decrease. I'm thinking along the same lines as other dietary treats (like candy or comfort food) that are probably not part of any theoretical "ideal" diet but which can still make people happy.