I really don't have a problem with people drinking, overall. I enjoy a drink (or three) now and again. I love beer. I don't think the world will end if I overdo it a bit (though I might wish it would), and I don't think that anyone who has a drink under the age of 18 (or 21, or whatever) is doomed to a life of raging alcoholism and an early death by liver disease.
I didn't drink when I was in high school. This wasn't so much a conscious decision as a result of never being invited to parties. My friends and I certainly had plenty of access to alcohol if we'd wanted it, but it never occurred to us. We were too busy with school/extra-curricular activities.
It might also be that we all had at least one alcoholic parent. When you've come home from school to find your father has driven his car through the ditch, over the front lawn and then passed out on the front step next to an empty bottle... well, you could say that the romance of alcohol is sort of gone. Of course, the reason that stands out is that it's not the norm, socially (even in WI). It's an embarrassment. If you see that sort of thing all around your community, it probably doesn't have the same impact.
ETA: My point, which I swear I was getting to...

So as far as enforcement, I don't think that the cops need to bust every teen party and ticket every kid who's touched a drop. And mostly, they don't. But I think that having the ability to confiscate alcohol from minors and/or cite them provides a bit of a deterrent, and can be a useful tool in dealing with kids who are developing problems. If you find a kid falling-down drunk once or twice, send them home. If you find the same kid passed out drunk four weekends in a row, then I think it'd be good if there were further options.