First of all, I’d prefer limited supervised drinking as a child grows up. As it is now, a person rarely learns to drink responsibly until they’ve made all the mistakes short of DUI and vehiclular manslaughter.
If children were taught to drink responsilbly and in moderation then imo the allure of binge drinking would diminish as would the aspect of the ‘forbidden fruit’.
Second, if one wants to base changing the law to 18 because one might be called upon to defend the country in uniform, then make the rule state that those that actually do defend the country in uniform legally drink, not just those who reach the age. Make it on actual merit, not potential merit.
Third, I’d disagree with your penalties and punishments all the way to Supreme Court simply because they are too severe for the crime committed. Lose a house (upwards of $200k fine) for underage drinking? No way, Jose.
I think potential merit is important. Enlisting in the military is a life-changing, possibly life-ending decision. If we say someone is old enough to make the decision to enlist, then they are certainly old enough to make the decision to buy and drink a beer.