Beer deserves a national day because it is the most widely-consumed alcoholic beverage in the United States. We are a beer-drinking nation. It's also central to the American economy: in addition to the giant mega-brewers (Anheuser-Busch, etc.) there are thousands of small craft breweries that support good jobs at the local level. There has been an explosion of public interest in high-quality beer in the last two decades, and a day that recognizes and encourages this interest is a net positive.
Having a National Beer Day is just a fun way to celebrate and have some fun. Beer has been around since the fifth millennium BC, making it one of the oldest beverages ever created by mankind, so why not celebrate that? There are many fine breweries in this country, many of which are micro-breweries, so any excuse to help out those small businesses is good.
A "National Beer Day" is nothing more than a marketing gimmick proposed by breweries and sellers of alcoholic beverages with the sole intent of promoting increased sales and consumption of these items. This nation already has serious problems related to alcohol and obesity and such a proclamation would only worsen these problems. There will inevitably be those who overindulge and there is sure to be an increase in drunk driving, underage drinking, and other dangerous alcohol-related events. We can also expect to see an increase in motor vehicle accidents and accident-related deaths. The negative consequences of such a "holiday" far outweigh any potential benefits and this idea should not be given serious consideration aside from the possible harm it would cause.
I feel that others have the opportunity to drink on a daily basis, so I do not feel that their needs to be a National Day, where everyone can get drunk and cause chaos throughout their towns. I do not feel that National Beer Day is needed or required whatso ever.