As others have mentioned, many cities around the world allow the consumption of alcohol in parks. Some places in Europe, Germany for example, allow you to consume alcohol just about anywhere. When I've gone there, I never noticed problems because of it. Like here, bottles and cans have a deposit so there's always people around to pick them up which solves the litter problem. If you look at it this way, there's already laws about being drunk and disorderly. So what's the difference between going to a bar, having X number of drinks then going to a park and having X number of drinks in the park?
They've finally changed the rules for events like Taste of the Danforth. It used to be you'd have to enter a tent or cordoned off area in order to have a drink. So what you'd have is people pounding a few drinks very quickly before going out to walk around. It makes more sense to allow people to walk around with a beverage and not feel rushed to consume a few at a time.
A bridge in Germany where people gather to enjoy local wines every afternoon. And yes, they're served in glass. How civilized.