I took a few pit mixes out of the local humane society last summer for "Doggy Day Out", basically an opportunity for dogs who need new homes to get exposure to the community and get away from the kennel for a few hours, and they were universally friendly, sweet dogs.
There's some selection bias, obviously, but their reputation is definitely overblown.
I was at a friend's place with some others from school, we were about 14-15 years old, his family had this seemingly sweet pitbull, always wanting to be pet, super playful but kind. That day it attacked one of our classmates, out of the blue, we were sitting on the backyard, the dog playing with some rope toys, brought it to us sitting, this guy picked up the toy to throw it and before he could even started the motion this pitbull jumped on his face and started attacking.
It was so jarring, unexpected, and brutal that I got traumatised for life from pitbulls, I don't like to be close to them, don't like when I'm biking and there's one without a muzzle being walked around, and I don't want to pet one as much as it can look super friendly and calm. Seeing how fast it could turn into a murder machine even when growing up in a loving family that never trained it to be a guard/attack dog, and probably never treated the dog badly, made me very anti-pitbulls.
Most dog attacks in the country I grew up in are from pitbulls, including a few kids killed every year, the statistics don't lie. The breed requires people who aren't assholes so it doesn't become dangerous, I don't trust owners to do that, even more when it's a breed for "macho" guys to show off at the same time.
I got bit by a dog a while ago and the thing that really woke me up was how unexpected it was. I generally think that I'm fairly observant and empathetic with animals. All B.S. aside I genuinely think I can tell when a dog is scared. The dog that bit me though, totally out of the blue. I saw it. No body language, no nothing - and I walked by it and next thing I knew it jumped out and bit my hand.
Since then if I see a strange dog and the option is there I keep plenty of distance between it and me no matter what I take to be it's state.
If we are to be pedantic I should have defined it as "most dog attacks causing serious enough harm to be reported" but I don't think it was needed to communicate the same thing.
They are banned in Ontario, Canada for a good reason and banned in UK for the same reasons.
The only time my dog was ever randomly attacked was a pitbull and you quickly learn talking to other dog owners how common this is. Nothing clears out a dog park like a pit bull showing up.
The ban isn't meaningfully enforced in much of the province [1], I see them a lot. I used to live in Ottawa, and their official site directly states "The City of Ottawa does not enforce the provincial ban on pit bulls" [2]. For those (legitimately) interested in a Canadian perspective on breed-specific legislation, there's a documentary by CBC's Fifth Estate on the subject [3].
Yep, that's why my dog still got attacked by one in Toronto. It's poorly enforced. The dog sprinted across an entire field without making a sound and pinned my dog hard by the throat.
Ontario also tried to remove the pitbull ban, after the usual "it's owners the owners" protests, but a bunch of attacks happened again so they reinstated it.
I suspect the reasons are (generously) keeping them out of the hands of people who would treat them poorly and perpetuate the stereotypes, or (less generously) ignorance and fear.
There are plenty of statistical studies out there that pit bulls specifically cause both a significant plurality of dog bites and significantly worse injuries than other dog breeds.
The word "pit" in "pit bull" refers specifically to a dog fighting arena where dogs are supposed to aggressively fight each other in a duel, possibly until one of them dies.
"pit bull" refers to a dog breed that was optimized for its performance (=more aggressive and dangerous) in the "pit".
How they're raised makes a big difference, but natural instinct is natural instinct. It's just like how chihuahuas were bred to be small, but pit bulls were bred to fight other dogs.
There's some selection bias, obviously, but their reputation is definitely overblown.