Most dogs that bite were not trained to be Aggressive - a lack of training is the problem
One of the hardest things in the world is for someone to change their behavior. It requires a conscious effort to STOP their typical habits and START new ones. If your dog has behavioral issues and you want that to change, you have to be ready to change, too. Something in your relationship is creating those problem behaviors and you have to be willing to change the way you live with your dog, for them to change their behavior living with you.
After a dog bite or attack in the news, all of the comments tend to say "it's the owners who taught them to be aggressive." Typically, the owner of the dogs say they are the nicest dogs and can not believe they would do "that." I do not believe that most people are training their dogs to be aggressive--actually that is the farthest thing from the truth. (Yes, there are cases of dogs not socialized well that are stuck in yards, on chains, or are running at large that go after people. However, recently in the news (and any of my clients that have loved pets who display aggressive behaviors) these dogs are not mistreated). If you were to take a step back to look at the relationship owners have with these types of dogs, they probably live, what the naked eye would call, the best life of LOVE. I can imagine these dogs are very spoiled by their owners--doing things like sleeping in bed, cuddling on the couch, cruising the house at large, pulling all over and sniffing everything on the walk, getting tons of affection and praise, and given TONS of freedom to do with it what they will. Every time someone knocks at the door or enters the house, these dogs are allowed to boldly rush up and jump, bark, and push their way into people's (or dog's) personal space. These dogs get a ton of freedom, have few rules (or at least few rules that would actually impact the dog's behavior--I imagine the owners do a lot of pleading verbal reprimands as the dog does something obnoxious), and very little accountability held for their behavior. To the naked eye, these look like dogs who are loved and living the best life because it is known how much then owner loves them and dedicates their life/home/property to their dog and letting it be "happy."
That might surprise you, because you were under the impression that dogs who bite must have been abused or mistreated. Nope! I know none of my clients have abused their dogs, and many have had them since puppies (so no rescue story of abuse present) and the dogs still act aggressively or have bitten people. (Even if a rescue dog had a bad experience, there are many things that can be done to move PAST their past and have a well-behaved dog. However, often people get stuck on their story, feel sorry for them, and follow the above mentioned "love protocol" out of pity, which unfortunately can create even more problems).
So! This is where we sit back and say, what must we do to take a very loved dog that bites people and make them stop? First thing we MUST do is realize (and admit) that the environment the dog lives in (and the people in that environment) contribute to the behaviors of the dog. That can be REALLY hard for many people because we are so emotionally invested in our dogs. But, the only way to see change in our dogs is to make change in ourselves and how we live with them.
Dog training and behavior modification is a matter of the dog learning new skills, as well as a family affair that requires everyone to change how they do things with their dog and begin recognizing the problems. It can be hard to change behaviors you didn't even know were a problem, especially if the majority of the interactions you have with your dog may be nurturing that bad behavior/insecurities/anxiety/etc. So, where do we start? First, we need to stop looking at our dogs as babies, children, or people--and look at them as the dogs they are! The furry, sharp-toothed predators they genetically are, that eat out of a bowl and poop in the yard. When we start to think of them as animals, we can start to see that guidance, protocols, and rules are necessary. These dogs don't know how to live in our human world without guidance, and if we let them do whatever they want they will do what they know best--be the animal they are and survive. It is our job to be a leader and advocate for our dog, and that means teaching them what we want them to do, setting rules and boundaries for them, and understanding that the lack of our authority presence creates a dog who doesn't know how to live in our human world. No one intends to raise their dog to be aggressive, but the lack of guidance, leadership, rules, boundaries, consequences, training, and authority (along with the surplus of freedom, constant affection, and some spoiling) creates a dog who is missing an advocate (and true friend) in their life. Because of this, many bad, often scary, behavioral issues develop.
If your dog is displaying aggressive or dangerous behaviors, please find a training professional to help you diagnose hat is going on and WHY :)