First........ I'm a Brit and I can assure you that the UK has some of the worst binge drinkers anywhere, of any age, as the unfortunate residents of many holiday resorts in the Mediterranean will tell you. We travel, we drink, we vomit. So 18 doesn't make them more responsible. It seems to be an Anglo Saxon thing too. Dunno why.
Drink Driving. This is the crux, and the figures speak for themselves. One main difference between the USA (drinking age 21) and Europe (18 or lower) is that most European young adults have access to public transport and copious amounts of taxis when drunk and therefore do not have such a necessity to drive everywhere. In the USA with so little mass transit, more kids drive and they drive much younger than in Europe. So the 'car culture' has to be taken into account.
On the other hand, I think it's quite ridiculous that I could be prosecuted for letting my kids (18 and 20) have a beer at home with a BBQ or a glass of wine with their dinner, at home or in a restaurant. I'd like to see the age reduced to 18 for drinking wine or beer with a restaurant meal when accompanied by an over 21. ie as a parent, I can take responsibility for buying them a drink with dinner. Keep the age at 21 for bars and clubs that don't sell food. And toughen up the drink driving laws for anyone caught over the limit. Automatic loss of license and - possibly - automatic jail time.
