I've seen unleashed dogs that are perfectly under control, and leashed dogs that are totally out of control.People walk their dogs on the school grounds where I go for exercise and as far as I know they are all good about cleaning up.
However...there's a sign that states animals are not allowed on school property. Also, there's a township leash law and a subset of the dog walkers allow their pets to walk along with them unrestrained. These rules don't ever appear to be enforced, so they are ignored.
One of the things that drives me crazy is when some adult lets their six or seven year old 'walk' their lab, or golden or even old english which are easily half (or more) the weight of the kid and a lot stronger. Even if the dog is friendly and tries to come bounding over to play with my dog it's a dangerous situation for the kid unless the dog is perfectly leash-trained.