Most aggression attributed to breeds is the result of a genetic trait that is either minimal or enhanced. We select for docility when we look at a bulls EPD stats. Of course environment can be a contributing factor.
We breed dogs for our own purposes. Most of the abilities we select for are based in the "prey drive". Herding, pointing birds, retrieving, and rat terriers going into a frantic hysteria to kill rats have all been the result of humans selecting animals that exhibited those abilities as a prey drive and being selected to be bred with each other... concentrating the genes involved in specific abilities.
It isn't that pits are bred to "attack humans". It's that they are bred to focus in an attack... no matter what they are triggered by. If they are triggered by another dog, a horse, or a duck, they focus on that trigger. They have been bred to focus and then to exhibit tenacity and keep focused until the target is destroyed. Training and human contact and environment are all factors... but the underlying genetics is where the tenacity genes are concentrated (or not)
In a litter of pups with a specific bred-in ability, whatever breed is involved, some pups may carry very little ability while others may carry enhanced ability. You can't look at the dogs and tell which of them will be better at their jobs than the others.
With traits that are expressed through multiple genes you can get a wide variety of potential. This is why crossbred pits may be more dangerous than purebreds. A crossbreed can carry more focus and and less tenacity... or it could be the opposite. This is why some dogs are more likely to bite more targets than others.
And you mentioned your own experience. the statistics on what percentage of pit types are involved in biting isn't well documented compared to what percentage are involved in human deaths, for obvious reasons. But the vast majority of pit will never bite, much less kill a person. That does not mean they don't have the genetic makeup that could be triggered.
I hope you are coming to this in good faith with a mind to consider the science involved. I'm giving you the benefit of the doubt by explaining this.