"Underage drinking is illegal. The reason it is illegal is because the people in their collective opinion say it should be."
I don't seem to recall a vote on the drinking age. Instead, federal funding for highways was withheld from States who delayed the federally mandated rise in the drinking age. Why is it an 18 year old can serve his country and not come back and have a beer legally? Does "collective opinion" think this is right?
PS - If the drinking age had remained at 18 the twins never would have landed in the papers for doing what the majority of college students do.
Do you not know how a democratic republic works? If you don't it would take far too long and someone with much more patience than I to teach you.