Without a BAL, how do you prove someone is intoxicated?
Dunno. As you say, there's no really good, objective way to know for sure.
But DUI is more about driving than public intoxication. Otherwise, bars and restaurants and clubs should have limits on how much alcohol they could serve a person, shouldn't they?
I don't think there's a good solution to the problem of keeping drunks off the road (short of some magical (perfect) car sensor that prevents operation by impaired drivers). As it stands now, it's perfectly legal (AFAIK) to drive to a bar, drink 15 shots of whiskey and drive home. The bartender won't get in trouble unless it's clear that the person is drunk. Even though that much whiskey would surely increase the BAC far beyond 0.08. By having the law written (as it apparently is in some cases) that DUI == (BAC > 0.08), then there seems to be a conflict.
Like you, I don't want drunks deciding on their own that they're fine and driving off and killing or maiming people. But either DUI convictions should be based on something more than just a BAC (something that illustrates actual intoxication), or the law should be called "Driving while BAC > 0.08". I'd have no problem with that - it's objective and there are reasonable reasons to have such a standard.
But I think determination intoxication or impairment should (somehow) be based on how a person acts, not on how much alcohol (or whatever) they've consumed or how much is in their blood. A 85 year old man who's zonked out on percocet is as much a danger as a 19 year old who's had 3 pitchers of beer...
Cheers,
Scott.