It just hit me that there's a rational explanation.
Being a good soldier and being a responsible drinker are two very different things. Just because you make a good soldier does not immediately imply you will make a responsible drinker.
Quite frankly, 18 is a pretty darn good age to start soldiering, but I know a TON of < 21yo who are not responsible, so my idea doesn't seem completely baseless.
There are also a ton of >21yo who are not responsible. That's not a good reason. Let's just ban alcohol because there will always be people that can't handle it.
Instead, why don't we look at the problem. The largest problem is that it's forbidden, so the majority of kids growing up have to sneak around and drink with other kids that are irresponsible. Telling a kid he can't do something just makes him want to do it even more.
If we introduce kids to responsible drinking at an earlier age, it wouldn't be so intriguing and they could learn a little bit about responsibility. You'd still have problems but I bet they'd be fewer and we could get back a little more freedom.
You are pretty much totally right. However, my only aim was to point out what I believe to be the fallacious nature of the argument that you should be able to drink if you can be a soldier. It plays off emotion well, but the criteria for making good soldier material are unrelated to the criteria for making a responsible drinker.
Being a good soldier and being a responsible drinker are two very different things. Just because you make a good soldier does not immediately imply you will make a responsible drinker.
Quite frankly, 18 is a pretty darn good age to start soldiering, but I know a TON of < 21yo who are not responsible, so my idea doesn't seem completely baseless.