The choice to drink or not pales in comparison to the other choices we face as adults. Having gone through college, I can say that the law is ineffective and prevented not one person from drinking after they left the parents nest. Dry campus rules had some effect. Law had no power. Anyone who stayed sober through school simply didn't care for alcohol. It seems strange to live in a society where I'm trusted to own a gun, raise children, and fight in war before I can have my first drink.
There is an argument that the brain is developing into your mid twenties and should be protected, but to that I say that its my brain, and my body. I'll make my own adult decisions pertaining to it and bask in my personal freedoms as an American. There's no reason for courts to be giving adults misdemeanors simply because they aren't 21 years old. If they disturb the peace sure, that affects others. If they are just having a couple beers at the wrong place and time, that's just ridiculous.
The National Minimum Drinking Age Act is a form of blackmail by the federal government that is based on antiquated ideals that have no place in our progressive society. States should be allowed to reduce their drinking ages to below 21. It's been over 30 years since this act was passed, and times have changed. It was passed during the Reagan administration, which was one of the most conservative of modern times.