I have all kinds of opinions (for and against) on this subject and couldn't figure out a way to type them all out in any graceful way- just kept jumping around. That said, I'll boil it down to one sentence.

Being a legal adult DOES NOT automatically make you responsible and mature enough to make responsible decisions- especially where alcohol is involved.

EDIT: I'd also like to add that 4 members of my senior class (all 18yo) died before graduation- 3 of them from alcohol related incidents.