I'm sure you've heard many a breed advocate utter this phrase: It's all in how you raise them. Meaning, vicious dogs are made, not born.
As an obvious Doberman advocate, you might be a little confused when you read my answer: That isn't necessarily true.
See, behavior has a genetic component as well as an environmental/socialized one. Breed an unstable dog, you have a high change of getting unstable puppies. Breed an aggressive dog, same thing. There's also the unfortunate situation when a reputable breeder did everything right. The parents are both of sound temperaments. The health tests are all in a row. The followed the rule of sevens for puppy raising. And then one of the puppies....just isn't right. Maybe just fearful, and that's a thing that can be managed with hard work and training, sometimes medication as well. But sometimes, one ends up with an aggressive dog, just out of the blue. Nothing to point at and say "This. This is what happened to that dog."
But that's just it. Reputable, responsible breeders try their hardest to stack the decks for their dogs. They want healthy dogs, physically and mentally. They pay attention to these things.
People who breed dogs for dollar signs don't. They throw two intact dogs together and X time later put 'em up on Craigslist or Kijiji (or advertise the litter on the AKC classifieds, if both dogs happen to have papers), "fully dewormed", maybe first shots if you're lucky. Genetic roulette, and also temperament roulette. Overbred, inbred, carelessly bred dogs are lined up in the shelters and caged in pet stores. And families don't know what they're bringing home.
This is a problem that transcends breed. Many, many people are frightened of pit bulls. And Dobermans. Rottweilers. Part of that is the size of the dog, part of it is breed image. They've been the Big Scary Mean Dogs in movies, the cultural doggie boogey man. A lab, though, if it decides to bite, can do just as much damage. Or a Golden Retriever. These are "friendly" breeds in the public eye, but bad breeding does not exclude them from temperament issues. Chihuahuas and Dachshunds too, but those little dogs can't do much damage, can they? Isn't it cute when they think they're big dogs? Funny story, bites from even small dogs can require a tetanus shot, cause nerve damage, or get infected.
No dog bites are funny. Bottom line. And a dog who lives his or her life fearful and anxious is not funny. An aggressive dog is scary. And owners sometimes have to make hard decisions regarding these dogs. I don't think anybody euthanizes a dog just for being fearful (I don't think. I obviously don't know), but a fearful dog can become a fear biting dog, and euthanasia frequently results from that. True aggression can be a nightmare to handle, and as a pet owner, who wants that? Constant management of a dog, for the "just in case"? I don't envy anybody that position.