I think the problem with pit bulls is that you can't tell from looking at them whether they are:
1. Normal, which is to say, not dog-safe, but bred to be utterly nonaggressive toward humans (under reasonable conditions, including basic training, being treated humanely, and not being frightened, ill, or in pain).
2. Descended from modern pit fighting and/or drug dealer protection lines. These dogs are bred for aggression, plain and simple, and have been observed trying to kill each other as puppies. Rescues find them extremely hard to handle because their natural state is psychotic. Luckily (at least for the pitties), druggies and dog fighters appear to be turning more to chows to get their super-aggressive dogs.
3. Born normal and raised by drug dealers, "having a mean dog makes me macho" jerks, or similar people who use brutality to make a normal dog into a killer. I knew one of these dogs once. He ended his life by jumping through a plate glass window in an attempt to attack his owner, who kept him chained up outside all the time and beat him with a belt "in order to make him a better guard dog." Some of these dogs can be rescued, retrained, and rehomed with people who treat them well.
4. Feral, from any bloodline; these dogs can be very dangerous because they don't have a natural fear of humans (being dogs) and they don't listen to humans either (being completely untrained). Feral life is very rough on a dog, BTW, and quite a few adult ferals who are captured and retrained settle happily into life in a human family. Interestingly, some of them appear to go through a period of nightmares and other symptoms of what in a human would be called PTSD.
I guess the moral of the story is, be very very careful around any dog that's wandering around without supervision, especially a big one.
Oh, and two dogs have attacked me with deadly intent in my life. (The psycho pit bull attacked my dog, but not me.) One was a puny, weedy-looking Labrador and the other was a teacup poodle about the size of my foot!
Back on topic: "If you love cats, you must hate dogs, or vice versa. If you like cats and I like dogs, we can't get along." Actually I like both and think that the ideal household should contain at least one of each, although I don't have a dog at present. I'm bipetsual.