At the age of 18, the American government sees you as an adult. But you aren't enough of an adult to have a glass of wine with dinner. You can move out on your own, but you can't have a beer to celebrate the new apartment. You can choose whether to continue your education or just go out and start a full time job. But you can't have a shot of whiskey with your boss during the interview!
At the age of 18, America has the right to ask you to fight for your country. They could reinstate the draft if it is needed, and they do recruit people as soon as they turn 18. So, the government tells you that you can go and die for your country, but no, you can't have a beer befor you take a scud missle to the teeth.
So my proposition is this: Either lower the drinking age in America to 18, or raise the age you can be recruited or drafted into the military to 21. I think it's only fair. Having a glass of wine with dinner isn't nearly as bad as dieing in a forgein country for America.