Linflas, consider this. How many people learn moderation automatically? Not very many people who do shots the first time or drink mixed drinks the first time have any clue on what moderation is. It can take a person quite a time, as in a year or two, to figure out what their "moderation" (read: tolerance) level is.
We all know that underage people drink. But, by the time they have reached legal drinking ages, many have taught themselves when to say when. I know that after drinking for two or three years from the age of 18 up till I was 21, I learned quite a few hard lessons. By the time I could legally purchase alchol, much of the flair associated with drinking was gone. Now, I'm not saying that it is ALL gone, but you won't see me tapping a keg on sunday nights anymore
Here's where the problem comes into play - if you drop the age to 18, people who have never really drank before are out on the streets stumbling around because of alcohol you can LEGALLY purchase. They haven't had a "break in" period before they could go out and drop their student loan checks at the bar down on the stip. You say that people know moderation. I say they do to, but they have access to the forbidden fruit before they are ready to handle it.
The other issue that I have is that there are MANY 18 year olds who are still in high school. Having somebody who can purchase alcohol legally on the high school football team is just asking for problems as well. Do you have any idea how much of an impact that will have? Just about any roadblocks that were in place for obtaining alchol in highschool have all been but eliminated. We don't need high school seniors able to buy beer for the underclassman.
Proms and Homecomings would be a nightmare(as if they weren't already). It just is not a good idea. 30 years ago many 18 year olds didn't go to college. You hopped out of highschool, got a job, got married, and bought a home. That process had been delayed now. More and more kids are going to college after highschool. It's another 4 years of reckless abandon. It's a time that begs of irresponsibility. Comparing the 18 year old of 25 years ago to the 18 year old of today is a night and day comparison.
Once again, I say that it is just a very bad idea.