No, this couldn't be further from the truth. Most people who think or say that "Pit Bulls" are inherently mean, have most likely never met one and rely on the inaccurate media hyped portryal of "Pit Bulls" as the basis of their opinions. Like any other breed of dog, the key areas of focus for ensuring a happy, well adjusted American Pit Bull Terrier as a pet are: owner education, proper breeding, socialization, and training. A break down in any one or more of these areas could lead to problems down the road.
The APBT is, contrary to popular belief, very human-friendly and will not naturally be aggressive towards humans. The APBT is, however, very loyal and eagar to please, so that if an owner wants a dog to be aggressive toward humans and reinforces this behaviour from an early age, the dog will most likely be aggressive towards humans as an adult.
Many people equate or confuse aggressivness towards other dogs with aggressivness towards humans. I have seen newspaper reports in which "concerned neighbors" are quoted saying things like, "This time it killed a stray cat; tomorrow it may be my children." Yet animal-aggressiveness is an entirely different thing from human-aggressiveness. There is no reason to infer from its killing a cat that a dog--any dog, not just an APBT--will ever show aggression toward human beings. Dogs can and do discriminate, even if irate neighbors cannot.
One of the most enduring urban legends involving dogs is the one about Doberman Pinscher's supposed tendency to suddenly "turn on" their loving owners. This violent change in behavior is said to be precipitated by a natural swelling of the dog's brain at a certain age (the exact age differs according to the retelling). Of course this legend has no basis at all in fact. The "pit bull" has replaced the Doberman Pinscher as the stereotypical "vicious breed," but the same human ignorance and credulity is behind the persistence of such legends.