When I was 17, toward the end of the Viet Nam war, the drinking age in Michigan was changed to 18 years old. This was in part based on the idea that if you were old enough to fight and die for your country, you should be allowed to drink alcohol. That lasted about 4 or 5 years before they changed it back to 21 again.
I find it very weird that more people don't bring up the argument of an 18 year old being able to fight for our country but not come home and celebrate with a beer.