Socializing your dog is an imperative part of being a responsible pet owner. Other dogs may not appreciate an unknown dog running up to them and invading their space, and similarly, people may not not like a dog doing this, even if that dog does this out of overly friendly enthusiasm. Remember, some people are legitimately afraid of dogs because of negative experiences. Service dogs and their handlers need to focus on going about their business and not being distracted by an unpredictable dog.
Be respectful of other people, their dogs, and the spaces of both.