Pit bulls were originally bred to be more dog reactive, and the people who breed them for fighting still do breed them for that (there are also reputable breeders who breed them for other things, and backyard breeders who breed for money, just for the sake of having puppies, or because they don't bother to spay/neuter). That being said, there are lots of more dog reactive breeds that aren't pits. If socialized early enough though, a lot of the time they can get along great with other dogs, or at the very least be trained to tolerate them. This is true for any breed. It's also true that a dog that isn't all around socialized properly will be much more likely to behave aggressively in general, usually out of fear. My backyard bred Boston terrier will snarl and lunge at strange dogs she meets out in public, but this is because she's afraid of them, which is because we didn't socialize her properly to dogs as a puppy and is exacerbated by her naturally fearful temperament.
Pits aren't naturally aggressive towards humans though, which is an annoyingly common myth. Traditionally the dogs bred for fighting would be culled if they showed aggression towards humans, because you want to be able to go in and drag the dog off the other dog it's mauling without your dog whipping around and slashing you. They only become a danger to humans through poor breeding and training, mostly the latter. People get "scary" looking dogs so they can go around looking tough then "train" them to "act mean." The problem isn't the dog in these cases, it's the idiot who shouldn't be owning one.
It annoys me when people take statistically uncommon incidents of pits attacking people (ignoring the fact that these are just about always pits owned by bad owners who poorly trained and socialized them often trying to encourage aggressive behavior in the first place) and use such anecdotal evidence as "proof" that these are bad evil dogs.
If people want to really attack a breed of dog for "aggression" they should go after Springer Spaniels and English Cocker Spaniels, especially show lines. Those breeds are more genetically predisposed in some lines to suffer from
rage syndrome. Rage syndrome causes a dog to suddenly snap and wildly attack anyone nearby with absolutely no warning for no reason. You can't train a dog out of it because it's neurological, not a training problem, so even the best trained dog with rage syndrome would still behave the same way, because the dog doesn't have any control over it and isn't aware of its actions. Why don't we go around banning spaniels? Because it's silly and it's rare, that's why.
If you're going to ban something, ban people who can't pass a basic test of knowledge and training ability from getting a dog. If idiots and people who know nothing about what they're getting into couldn't own dogs, it would solve the problem.