I'm not a big pitbull fan either, and those pictures represent the reason why. They are instinctive fighters based on purpose-bred genealogy, and when those instincts get turned on, they are difficult to turn off, which is why the breed can be deadly to people and other animals.
Yes, I know, some of you know or have wonderful, sweet pitbulls. But whether you have seen it or not, every member of the breed has the genetic capacity to replicate what is shown in the picture above.
Yes, I know many different breeds of dogs can hurt people or other animals, but how many breeds of dog do you know that will continue a fight to the extent shown above? Couple that with the dog's instinctive fighting drive to bite the head and neck area with it's incredibly powerful jaws, and you have a very deadly potential in something that cannot be guarenteed to be under positive control 100% of the time.