Just to have my say on this matter.
Given that not everyone likes dogs, and how many people of different ages and vulnerabilities we pass on our walks, mine stay on lead at ALL times.
I know my dogs well, and know what to expect from them, but their moods change quickly, and an off lead dog can cause some scary reactions.
Even on lead I have had adults run out in front of buses to avoid mine, a child collapse in terror and start screaming, people regularly cross the road to not to pass them (dogs are ALWAYS on my inside against a wall etc)
I can't begin to imagine how much worse these situations could have been if the dogs were off lead.

In short, dogs belong on a lead, unless being exercised in an area away from other people who may come into contact with the dogs against their (humans) will.