It's not as simple as this, so I'm going to break it down more.
The American Pit Bull Terrier (APBT), the only true "pit bull," is described as being confident, eager to please, and extremely friendly, according to the UKC breed standard. They have been noted to love people, especially children. Aggressive behavior towards humans is highly undesirable. However, dog aggression (DA) and small animal aggression (SAA) are common and within standard. This means that it's normal and acceptable for APBTs to exhibit aggressive behavior towards dogs, cats, squirrels, rabbits, etc. So aggression is part of their breed standard.
The term "pit bull" has been watered down over the years. It has come to reference a dog type rather than a breed, which should not be the case. Backyard breeders (bybs) have diluted the breed and have allowed dogs to be born and bred that do not fit the standard. These undesirable dogs continue to be bred, some exhibiting uncharacteristic behavior for their standard, and this is where human aggression (HA) has become a bigger issue. Pair this with people who do not socialize and train their dogs properly (ex. no emphasis on neutrality, punishing a growl, etc), and who do not know dog behavior (ex. whale eye, lip licking, different tail wags, etc), and this is a recipe for disaster.
There are no bad dogs in the sense of right and wrong. Dogs don't have a moral compass like humans do. But there are aggressive dogs out there. There are different types of aggression that dogs display. And that is okay! Dogs are individuals and have the right to exhibit their feelings. Aggressive dogs can be highly trained, aggressive dogs can be in public (as long as they are well managed), aggressive dogs can live long, amazing lives.
To deny the existence of aggressive dogs is doing them a disservice. Aggressive dogs need an owner willing and able to fulfill their needs and to advocate for them. Most people do not want to deal with that or are not equipped to deal with that, which is fine. But denying aggression can lead to someone getting a dog that is not a good fit for them, and that is, again, where problems occur and bites happen.
Being open and honest about dogs and their personalities, preferences, characteristics, etc is what will help them live a good and safe life.
