I don't usually like to say anything on threads like this as I find they can end up a bit tit-for-tat, but having said that I would like to point out that I was brought up around dogs - many breeds.
My family and I have owned a Chihuahua, a Jack Russell Terrier, A GSD, a Dobie, a King Charles Spaniel a Staffie x Boxer and one of her pups (father was King Staffie).
I found that the chihuahua was the most vicious of the bunch and in fact once leapt off the bed and bit me so hard that he was hanging from my stomach and scarred me through my leather coat just because I dared walk into my mothers room.
My Staffie x Boxer looks like a pit, and her offspring that is my son's dog even more so due to the King Staff in him. Both these dogs are the most gentle (although nutty! - and that means excitable) dogs I have come across. The mum was introduced to DS when he was 18mths old and they are the best of friends - to the point where he used to cry if she didn't go bed with him. He pulls her ears, tail etc and even used to sit on her back and pull her head up by her neck or her lips to give her a kiss. Dangerous?? Methinks not.
DS's aunt also had 2 staffies. One was named Arnie after Arnold Schwarzenegger (sp?) as he was huge and looked intimidating. Dangerous?? Hardly, the thing was scared of his own shadow!! He couldn't be walked at night due to the shadows and how much he'd poop himself! He lived in a house with 3 children and was there before all them were born. Dopiest dog ever .
There ARE some dangerous dogs. Some are dangerous by nature, BUT if raised right they are very good natured and predicatble. Unfortunately it the irresponsible owners who are "dangerous", the ones who never discipline or who actually train the dog to be nasty.
As for parks, in a no dog area, then of course they should not be there. But a public, open park is precisely that. Public and open to all - including dog owners who choose to exercise their dogs there.
And why shouldn't an obedient dog be let off the lead? Actually, dogs such as Staffies should be let off for a good run. They need the exercise and a short walk at our pace on a lead does not pffer adequate exercise for such breed.
I think there needs to be tougher penalties for the owners IMO.