From when I was 4 to 12 years old, my family lived next door to a family that raised pit bulls as guard dogs. While the parents of the family were at work, my younger sister and I would throw sticks over the fence for the gaggle of puppies to fetch back to us. They were adorable!
I was friends with the child of that family but when I visited we were forbidden from playing with the puppies because we might "ruin them". It never stopped me from playing with them through the fence when the breeders were away, though.
A few months later the puppies had gotten bigger, and disappeared for a few days. When they came back, they wouldn't play anymore, only jumping at the fence and trying to attack us. I don't know what they did to them, but they were completely changed.
People in the neighborhood reported them several times, and eventually they were banned from owning any pit bulls, and eventually from having any dogs at all, by either animal control or the neighborhood association, I can't remember which. Regardless, the only thing that ban changed was that they kept their dogs inside from then on, as I found out on a playdate.
Soon after my parents called in and reported the locked up dogs, we moved away, but I still worry that they're abusing sweet dogs to make them into guard animals.
Sorry for the rambling story! Anyway, my point was that the bans should be on people misusing dogs, not the breeds themselves!