First post guys, sorry it it's a bit of a ramble.
First off, I think it's important to establish exactly what you mean by "drinking" age, and whether it should apply just to buying alcohol or to consumption period. Where I am in Manitoba (Canada), the age for buying alcohol is 18, the same as our age of majority. However, kids are allowed to drink in restaurants (but not pubs/bars) so long as their parents are with them, and drinking at home is outside the jurisdiction of the government, unless of course someone makes a noise complaint or something.
When I was in high school here our alcohol education focussed on safety and knowing your own limit - it was never suggested, not even by the most conservative of my teachers, that we not drink. The people supporting the current age of 21 seem to believe that millions of otherwise adult Americans are going to somehow just stay pious, toe the line and not touch a single drop of what their parents (before 1986) freely enjoyed. Is this not far too idealistic? If the law is there to be broken - particularly a piece of low-hanging forbidden fruit like this one - then people are gonna break it, and because no-one ever explained to them how to pace themselves or be just a tiny bit responsible, they are gonna overdo it and possibly put lives in jeopardy. I agree with those who say that education and upbringing is more important than neuroscience. Twenty-one is a completely arbitrary number, and for every study that pegs full development at Chosen Age of Responsibility x, there is another that puts it at Chosen Age of Responsibility y.
I don't want to jump on the anti-American bandwagon or anything, but the 18, 19 and 20 year-old Americans that come up here to go clubbing cavort around like 15, 16 and 17 year-old Canadians would, chugging stuff down like the Apocalypse is coming and acting like complete idiots. For us, we enjoy drinking, but the novelty factor is largely gone once you hit 18, and we enjoy drinking for what it is. Binge drinking is a problem here too, but it's much less significant as a major social ill. Does anyone remember really wanting to buy a game that was rated M/18+, and how it being forbidden just sweetened the deal? It's the same with any age-limited activity.
You guys are going in the right direction with the population density & DUI factor, but are a little off the mark in your comparisons between countries. Even though Canada as a whole has a way lower population density than the US because of our empty north, we a) live almost exclusively in cities, b) live at a higher population density in those cities, and c) are less dependent on our cars. Even in Winnipeg, the most driving-obsessed and spread out city in the country, only two thirds of driving-age people use cars to get around, and buses run late into the night. Because we live closer together, cab fares are cheaper, and people who are too drunk to drive but still making sense are less likely to go "ah screw it, I'm not paying ___, I'll just drive" (it happens, and when the bus isn't there are a backup it happens even more). If people want to get drunk and be idiots (legal or not), it's their right to do so and face the consequences, but it is not their right to threaten the safety of others.
In a way, the US is having to lie in the bed it made. By choosing to build a society post-WWII where everything is built with cars in mind, where every city has a million fat freeways cutting through it, and a person's usefulness to society is entirely dependent on having access to their own private car just to function in day-to-day life (even when they are a child!), it's very hard to prevent the more tragic outcomes. And it's hard to hand down the DUI penalties that should be handed down - losing your license, preferably for a good year or two - because taking away someone's privilege to drive for that long equates to complete house arrest. Up here, a yearlong license suspension is the minimum sentence for merely blowing over 0.08%, and three, five and ten year driving bans are not uncommon.
Leaving the drinking age at 21 is a misguided and ridiculous move that serves nothing except to delay the moment where the idea of drinking responsibly finally hits people upside the head, and puts others in danger for no good reason. Sure, car dependence doesn't help the situation either, but I think that the US should toughen up DUI enforcement and through responsible drinking education and a sane drinking age make the most at risk group - the people 18-20 - into less of a liability.
So actually allowing them to drink from 21 is some kind of a favor.
