If 18 year olds are old enough to join the army and smoke cigarettes, then they should be old enough to purchase alcohol. Banning alcohol sales to people 18 to 20 is ineffective to stopping abuse and only leads to more crimes and excess burden to officers who try to enforce.
The research of alcohol's permanent effect on the brain at a younger age is insignificant, if accurate. Should the government band fast food and smoking because of long term effects on people or let Americans make the choices they deserve to make. Legalize alcohol purchases at 18 and give young adults the privilege they deserve.