Why, do you suppose, drinking "in public" is illegal in most states?

Not that I’m a great proponent of drinking, but It seems like a strange law, where it’s fine to drink in restaurants/bars/clubs, etc – but you can’t walk down the street drinking a beer. Maybe you can’t walk drinking a beer at all, but that’s separate… Then of course you can smoke only outside in public… but not in restaurants or bars (in some states, NY and IL at least.)
What do you suppose is the reasoning behind that sort of law? It’s perfectly acceptable to drink outside in most of Europe as I recall.