I have an incredibly sweet and affectionate English Setter. She would never bite or be aggressive with anyone. She is conflict averse, so she is excellent with children (will walk away even if children pull on her). Can't ask for a better or more beautiful dog (she is a Blue Belton in color).
But guess what? I live in a very nice neighborhood, with lots of trails. I can't for a moment let her off leash in my neighborhood. She has a high prey drive for birds and squirrels (to flush them, not to hurt them), and she is incredibly fast. If let loose, she could easily run over someone, perhaps even a child. Now, if she unwittingly hurt someone, she would feel awful (she is that sensitive), but it doesn't matter. She simply cannot go off leash, and it is unfair to my neighbors and to the dog to do so. In my neighborhood the dogs are almost to a one friendly. But any dog diving at your legs while running is a danger and a nuisance.
I wish I was a bit more of an expert with dogs, especially since i have this gem of a dog. But a simple rule applies - with your dog, treat others as you would like to be treated - leash the dog.
By the way, there is a beautiful state arboretum 40 miles away which is expansive and permits dogs to run off leash away from the main academic building (UVa owns it). I have let my dog run there, and there isn't a problem as there is so much room the dog doesn't come close to the few runners (there should be more at this place, by the way, as it is that nice). But in the neighborhood? Leash and courtesy. By the way, she is a good running dog, but not a great one. She is a bit more of a sprinter.