They were bred for fighting, and more specifically, for grabbing the face of their opponent. From a website that describes the history of pitbulls, "These breeds were originally developed as fighting dogs from cross breeding bull-baiting dogs (used to hold the faces and heads of larger animals such as bulls) and terriers."

I have owned many bird hunting dogs. Brittanys, German Shorthair Pointers, and now a Wirehaired Pointing Griffon. These dogs have pointing deep in their DNA. It doesn't take much, if any, training from me for them to go on point when they find a bird. So, if my dogs don't need training to go on point, which is what they were bred for, why do pitbull defenders think that pitbulls aren't going to resort to their very nature of attacking and grabbing the face/head of some other dog or even a child?

There is a reason that most insurances will not insure a homeowner that has pitbulls. The liability is too great. If you are still defending pitbulls, you are either lying or you have your head in the sand.