Why are pit bull owners full crap, always blaming the owner.

My neighbor had two pits on chased my sister and killed my dog. The front door neighbors pit bull chased me. Then another pitbull chased me. In these four encounters with this dog breed something bad happened, and usually you get then same old story from the pitbull owner "she is sweet dog she wont bite "until she does, what pisses me off too is how if such dog mauls someone they will hardly get a punishment. There is no reason why a dog shouldn't be on leashed. Also my friend had a pit and the dog will get aggressive around me and he will tell she doesn't bite. A few close encounters with this dog breed and they have shown aggression towards someone or something.