As much as we all hate to admit it, every breed of dog was bred to do a job. If you do research, then you will discover that pit bulls and other similar dogs were bred by dog fighters, for dog fighting. Thus, they CAN BE aggressive. I'm not saying they should be banned, nor am I saying I hate them, but they should only be kept by RESPONSIBLE owners that can provide proper care, (Preferably with a dog license!) and have done RESEARCH on the breed and the problems it may cause. The same should go for any dog, and any pet in general.
TL;DR: Be responsible with possibly dangerous dogs, and any pets.