I don't care that they're Pit Bulls.
I don't care if they were my beloved Kelpie.
The fact is that they were out wandering. People know if their dogs are aggressive. These owners would have known these dogs weren't canine socialised. These things don't just 'happen'.
I agree Occy, you have to have a licence to own more that 4 dogs. Someone who puts enough effort into a licence, puts enough effort into the training of their dog. Obviously, these arn't amazingly(is that a word) brought up dogs. I would not be surpised if they were being used for breeding.