1) Alcohol education starts at home, and yet we have outlawed the act of learning in the average home (most people move out long before they turn 21 and therefore, under the law, parents have no chance to permit legal responsible drinking in the home).
2) When people learn from their peers rather than older adults like parents, they learn in an inherently more irresponsible way. The drinking age of 21 has promoted a culture of secret, binge drinking by 18-20 year olds.
3) We say that 18 year-olds are adult enough to kill and die in the armed forces, change the course of a nation in the voting booth, judge other adults on a jury, be prosecuted as an adult, enter into binding contracts, operate automobiles and heavy machinery, smoke tobacco, own and operate a business, have a bank account and credit card, own a house, be married and have a family of their own. To say they cannot have a beer is highly, absurdly inconsistent.
4) Treating these adults like infants and then expecting adult behavior is illogical.
5) As the highest drinking age in the world, the U.S. legal age of 21 has utterly failed to prevent the 82 percent of 18-20 year-olds who drink alcohol from doing so. This is because it is an unrealistic law, like setting a freeway speed limit at 40mph and arresting everyone who goes over it.