All of the bluster about alcohol (binge drinking etc.) ignores one fact: for 3/4 of an undergraduate population alcohol is forbidden fruit due to the 21 age restriction. Yes some bars will allow 18-and-up in and we all know that (wink wink) these 18+ customers MIGHT have a tipple or two.'
But prohibition and an arbitrary age limit simply increase demand. In the case of college students the demand and the prohibition set up a challenge, a game to be won at all costs. Consumption of alcohol in moderation is, or was, a rite of passage into adulthood. Social drinking is called that for a reason. When alcohol becomes contraband then access to that contraband can become an obsession. When the object of the obsession is obtained the next logical (?) step is to go absolutely hog-wild. Overconsumption becomes the norm because in the back of the mind of every underage drinker is "when and where will I have access to alcohol again?"
The 21 drinking age has failed on two fronts: it has failed to prevent or even reduce consumption; indeed, it has increased it in many cases. Worse, it has created hundreds if not thousands of unsupervised speakeasies in the form of dorm rooms, apartments, off-campus houses, etc. where social drinking i.e. a public display of being able to consume and still function as a rational human being is nowhere to be found. Instead, interaction is limited to drinking-oriented games (e.g. beer pong) and constant exhortations to consume stupor-inducing quantities of alcohol (beer bongs, shots, etc.).
In sum, the 21 drinking age is an overreach that stands the process of socialization on its head and forces students who choose to drink into a state of arrested development. They remain children but they are children with easy access to oceans of beer and spirits rather than young adults who frequent licensed venues in order to drink, yes, but also to (hopefully) continue the process of maturation via interaction.